332 Check Engine Codes Explained

Quick answer: A check-engine light is a code, not a diagnosis. The code tells us which system complained; it does not tell us which part failed. Below are 332 common engine, transmission, ABS and network codes we see at RS Autowerks in Wayne, NJ, what each one means in plain English, the usual causes from cheapest to most expensive, how urgent it is, and what we actually do about it. We use factory-level diagnostic tools (BMW ISTA, VCDS/ODIS for Audi-VW, Autel for everything else) and we fix the cause, not just clear the light.

Check engine light on? Bring the code, we do the thinking.

Full-system scan, live data, and an itemized quote that separates “needs fixing” from “can wait.” Failed NJ inspection? The checkup and estimate are free. RS Autowerks · 145 Garside Ave, Wayne, NJ 07470 · Mon–Sat 9 AM–5 PM

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Most common codes: full pages

We wrote dedicated pages for the five codes we see most in Wayne, NJ, with what they mean, what could be wrong, and how we diagnose them: P0420 catalytic converter, P0300 random misfire, P0171 system too lean, P0455 EVAP large leak and P0700 transmission fault.

How to read a code

P = powertrain (engine and transmission), B = body, C = chassis (ABS, steering), U = network (modules not talking). P0xxx codes are the same on every make; P1xxx codes are manufacturer-specific. “Bank 1” is the side of the engine with cylinder 1; “Sensor 1” is before the catalytic converter, “Sensor 2” is after. A flashing check-engine light means an active misfire: stop driving and call, because it can destroy the catalytic converter in minutes.

Misfire codes (P0300–P0308)

A misfire means one or more cylinders isn’t burning fuel properly. The last digit tells you which cylinder (P0301 = cylinder 1). P0300 is a random/multiple misfire.

P0300 – Random / Multiple Cylinder Misfire

What it means: The engine is misfiring on more than one cylinder or the computer can’t pin it to one.
Common causes: Worn spark plugs, weak ignition coils, vacuum leak, low fuel pressure, dirty injectors, low compression, bad engine mounts on some cars.
How urgent: High if the light is flashing.
What we do: We check live misfire counts per cylinder, test plugs/coils, smoke-test for vacuum leaks and check fuel pressure. Usually plugs and a coil or a vacuum hose. A flashing light means stop driving: it can destroy the catalytic converter.

P0301 – Cylinder 1 Misfire Detected

What it means: Cylinder 1 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 1 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0302 – Cylinder 2 Misfire Detected

What it means: Cylinder 2 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 2 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0303 – Cylinder 3 Misfire Detected

What it means: Cylinder 3 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 3 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0304 – Cylinder 4 Misfire Detected

What it means: Cylinder 4 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 4 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0305 – Cylinder 5 Misfire Detected

What it means: Cylinder 5 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 5 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0306 – Cylinder 6 Misfire Detected

What it means: Cylinder 6 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 6 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0307 – Cylinder 7 Misfire Detected

What it means: Cylinder 7 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 7 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

P0308 – Cylinder 8 Misfire Detected

What it means: Cylinder 8 is not firing consistently.
Common causes: Spark plug, ignition coil or coil boot on that cylinder, a clogged or leaking injector, low compression or a valve issue on that cylinder.
How urgent: High if flashing, medium otherwise.
What we do: We swap the coil from cylinder 8 to another cylinder and re-scan: if the code moves, it’s the coil. Then plug, injector and compression on that cylinder. We replace only the part that’s faulty.

Fuel trim and air/fuel mixture codes

The computer constantly adjusts how much fuel it adds. When it has to add or remove far more than normal, it sets a “lean” (too much air) or “rich” (too much fuel) code.

P0171 – System Too Lean (Bank 1)

What it means: Too much air or not enough fuel on bank 1.
Common causes: Vacuum leak (intake boot, PCV hose, intake gasket), dirty MAF sensor, weak fuel pump, clogged filter, leaking injector O-ring, exhaust leak before the O2 sensor.
How urgent: Medium.
What we do: Smoke test for vacuum leaks first (the most common cause), clean the MAF, check fuel pressure. Most lean codes are a cracked hose or a dirty sensor, not a fuel pump.

P0174 – System Too Lean (Bank 2)

What it means: Same as P0171 on the other bank of a V6/V8.
Common causes: Same causes as P0171; if both P0171 and P0174 are set together, think vacuum leak, MAF or fuel supply rather than one cylinder.
How urgent: Medium.
What we do: Same process as P0171. Both banks lean together points to something shared: intake leak, MAF or fuel pressure.

P0172 – System Too Rich (Bank 1)

What it means: Too much fuel or not enough air on bank 1.
Common causes: Leaking injector, high fuel pressure (bad regulator), faulty MAF, stuck-open purge valve, coolant temp sensor reading cold, clogged air filter.
How urgent: Medium.
What we do: Live-data check of fuel trims, MAF and coolant temp, then injector and pressure tests. Rich running wastes gas and kills catalytic converters, so we don’t let it sit.

P0175 – System Too Rich (Bank 2)

What it means: Same as P0172 on bank 2.
Common causes: Same as P0172.
How urgent: Medium.
What we do: Same as P0172.

P0087 – Fuel Rail/System Pressure Too Low

What it means: Fuel pressure is below what the computer commands.
Common causes: Weak fuel pump, clogged fuel filter, failing high-pressure pump on direct-injection engines, pressure sensor.
How urgent: Medium to high.
What we do: Fuel pressure test under load, filter check, then pump or sensor. Common on direct-injection Audi/VW, BMW, Ford EcoBoost and GM engines.

P0191 – Fuel Rail Pressure Sensor Circuit Range/Performance

What it means: The fuel pressure sensor reading doesn’t make sense to the computer.
Common causes: Faulty sensor, wiring, or an actual pressure problem.
How urgent: Medium.
What we do: We compare the sensor to a real gauge before replacing anything.

P0201 – Injector Circuit (Cylinder 1)

What it means: Electrical fault in the injector circuit for cylinder 1 (P0202–P0208 are cylinders 2–8).
Common causes: Injector coil failed, connector, wiring, or the driver in the ECU.
How urgent: Medium.
What we do: Resistance and command tests on the injector and harness. Usually the injector or its connector.

P0202 – Injector Circuit (Cylinder 2)

What it means: Electrical fault in the injector circuit for cylinder 2.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 2 and its harness. Usually the injector or connector.

P0203 – Injector Circuit (Cylinder 3)

What it means: Electrical fault in the injector circuit for cylinder 3.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 3 and its harness. Usually the injector or connector.

P0204 – Injector Circuit (Cylinder 4)

What it means: Electrical fault in the injector circuit for cylinder 4.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 4 and its harness. Usually the injector or connector.

P0205 – Injector Circuit (Cylinder 5)

What it means: Electrical fault in the injector circuit for cylinder 5.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 5 and its harness. Usually the injector or connector.

P0206 – Injector Circuit (Cylinder 6)

What it means: Electrical fault in the injector circuit for cylinder 6.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 6 and its harness. Usually the injector or connector.

P0207 – Injector Circuit (Cylinder 7)

What it means: Electrical fault in the injector circuit for cylinder 7.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 7 and its harness. Usually the injector or connector.

P0208 – Injector Circuit (Cylinder 8)

What it means: Electrical fault in the injector circuit for cylinder 8.
Common causes: Injector coil failed, connector, wiring, or the ECU driver.
How urgent: Medium.
What we do: Resistance and command tests on injector 8 and its harness. Usually the injector or connector.

Oxygen sensor and air/fuel sensor codes

Oxygen sensors measure the exhaust so the computer can fine-tune the mixture. Bank 1 is the side with cylinder 1; sensor 1 is before the catalytic converter, sensor 2 is after.

P0130 – O2 Sensor Circuit (Bank 1 Sensor 1)

What it means: Upstream oxygen sensor on bank 1 isn’t responding properly.
Common causes: Aged sensor, wiring/connector, exhaust leak, heater failure.
How urgent: Medium.
What we do: Live-data graph of the sensor; a lazy sensor gets replaced, a wiring fault gets repaired. Exhaust leaks are checked first.

P0131 – O2 Sensor Low Voltage (Bank 1 Sensor 1)

What it means: Upstream sensor stuck reading lean.
Common causes: Exhaust leak, vacuum leak, failed sensor, wiring short.
How urgent: Medium.
What we do: Check for leaks, then sensor response. Often a leak, not the sensor.

P0133 – O2 Sensor Slow Response (Bank 1 Sensor 1)

What it means: The upstream sensor reacts too slowly.
Common causes: Aged/contaminated sensor, exhaust leak, oil or coolant contamination.
How urgent: Medium.
What we do: Usually the sensor is worn out; we confirm with live data before replacing.

P0134 – O2 Sensor No Activity (Bank 1 Sensor 1)

What it means: The sensor isn’t producing a signal at all.
Common causes: Failed sensor, unplugged connector, blown heater fuse, broken wire.
How urgent: Medium.
What we do: Check fuse/connector first, then replace the sensor.

P0135 – O2 Sensor Heater Circuit (Bank 1 Sensor 1)

What it means: The sensor’s built-in heater isn’t working.
Common causes: Heater element failed inside the sensor, fuse, wiring.
How urgent: Low to medium.
What we do: Fuse and wiring check, then a new sensor. Inexpensive on most cars.

P0136 – O2 Sensor Circuit (Bank 1 Sensor 2)

What it means: Downstream (after-converter) sensor fault.
Common causes: Aged sensor, wiring, exhaust leak after the converter.
How urgent: Low to medium.
What we do: Sensor and wiring test; the downstream sensor mostly monitors the converter, so the car usually runs fine.

P0138 – O2 Sensor High Voltage (Bank 1 Sensor 2)

What it means: Downstream sensor reading rich/high.
Common causes: Sensor failure, wiring short to voltage, rich running engine.
How urgent: Low to medium.
What we do: Wiring check, then sensor.

P0141 – O2 Sensor Heater Circuit (Bank 1 Sensor 2)

What it means: Heater in the downstream sensor isn’t working.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low.
What we do: Usually a sensor; we verify the fuse and circuit first.

P0150 – O2 Sensor Circuit (Bank 2 Sensor 1)

What it means: Upstream sensor fault on bank 2 (P0151–P0155 are the bank-2 versions of the codes above).
Common causes: Same as bank 1.
How urgent: Medium.
What we do: Same process as bank 1.

P0155 – O2 Sensor Heater Circuit (Bank 2 Sensor 1)

What it means: Heater fault, bank 2 upstream.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low to medium.
What we do: Same as P0135.

P0161 – O2 Sensor Heater Circuit (Bank 2 Sensor 2)

What it means: Heater fault, bank 2 downstream.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low.
What we do: Same as P0141.

P2195 – O2/Air-Fuel Sensor Signal Stuck Lean (Bank 1 Sensor 1)

What it means: Wide-band air/fuel sensor reading lean.
Common causes: Vacuum leak, exhaust leak, failed air/fuel sensor, low fuel pressure.
How urgent: Medium.
What we do: Leak tests first, then sensor. Common on Toyota, Honda, Nissan and Subaru.

P2196 – O2/Air-Fuel Sensor Signal Stuck Rich (Bank 1 Sensor 1)

What it means: Wide-band sensor reading rich.
Common causes: Leaking injector, high fuel pressure, failed sensor, purge valve stuck open.
How urgent: Medium.
What we do: Fuel system and sensor checks.

P2270 – O2 Sensor Signal Stuck Lean (Bank 1 Sensor 2)

What it means: Downstream sensor reading lean.
Common causes: Exhaust leak near the sensor, sensor failure, converter issue.
How urgent: Low to medium.
What we do: Exhaust leak check, then sensor.

P2271 – O2 Sensor Signal Stuck Rich (Bank 1 Sensor 2)

What it means: Downstream sensor reading rich.
Common causes: Sensor failure, rich engine, converter.
How urgent: Low to medium.
What we do: Same as P2270.

P0151 – O2 Sensor Low Voltage (Bank 2 Sensor 1)

What it means: Bank 2 upstream sensor stuck lean.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0153 – O2 Sensor Slow Response (Bank 2 Sensor 1)

What it means: Bank 2 upstream sensor reacts too slowly.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0154 – O2 Sensor No Activity (Bank 2 Sensor 1)

What it means: Bank 2 upstream sensor has no signal.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0156 – O2 Sensor Circuit (Bank 2 Sensor 2)

What it means: Bank 2 downstream sensor fault.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0157 – O2 Sensor Low Voltage (Bank 2 Sensor 2)

What it means: Bank 2 downstream reading low.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0158 – O2 Sensor High Voltage (Bank 2 Sensor 2)

What it means: Bank 2 downstream reading high.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0137 – O2 Sensor Low Voltage (Bank 1 Sensor 2)

What it means: Bank 1 downstream reading low.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0139 – O2 Sensor Slow Response (Bank 1 Sensor 2)

What it means: Bank 1 downstream reacts slowly.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0140 – O2 Sensor No Activity (Bank 1 Sensor 2)

What it means: Bank 1 downstream has no signal.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0132 – O2 Sensor High Voltage (Bank 1 Sensor 1)

What it means: Bank 1 upstream stuck rich.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0152 – O2 Sensor High Voltage (Bank 2 Sensor 1)

What it means: Bank 2 upstream stuck rich.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P2197 – O2/Air-Fuel Sensor Signal Stuck Lean (Bank 2 Sensor 1)

What it means: Bank 2 wide-band sensor reading lean.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P2198 – O2/Air-Fuel Sensor Signal Stuck Rich (Bank 2 Sensor 1)

What it means: Bank 2 wide-band sensor reading rich.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P2237 – O2 Sensor Positive Current Control Circuit (Bank 1 Sensor 1)

What it means: Wide-band sensor control circuit fault.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P2238 – O2 Sensor Positive Current Control Circuit Low (Bank 1 Sensor 1)

What it means: Wide-band sensor circuit low.
Common causes: Aged or failed sensor, wiring/connector, exhaust leak near the sensor, engine running lean or rich.
How urgent: Low to medium.
What we do: Exhaust leak check and live-data test before replacing the sensor.

P0030 – HO2S Heater Control Circuit (Bank 1 Sensor 1)

What it means: Oxygen sensor heater control circuit fault.
Common causes: Sensor heater, fuse, relay, wiring.
How urgent: Low to medium.
What we do: Fuse/relay and circuit test, then sensor.

P0036 – HO2S Heater Control Circuit (Bank 1 Sensor 2)

What it means: Downstream heater control circuit fault.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low.
What we do: Circuit test, then sensor.

P0050 – HO2S Heater Control Circuit (Bank 2 Sensor 1)

What it means: Bank 2 upstream heater circuit fault.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low to medium.
What we do: Same as P0030.

P0056 – HO2S Heater Control Circuit (Bank 2 Sensor 2)

What it means: Bank 2 downstream heater circuit fault.
Common causes: Sensor heater, fuse, wiring.
How urgent: Low.
What we do: Same as P0036.

P0031 – HO2S Heater Circuit Low (Bank 1 Sensor 1)

What it means: Heater circuit low.
Common causes: Sensor heater, wiring.
How urgent: Low to medium.
What we do: Circuit test, sensor.

P0032 – HO2S Heater Circuit High (Bank 1 Sensor 1)

What it means: Heater circuit high.
Common causes: Sensor heater, wiring short.
How urgent: Low to medium.
What we do: Circuit test, sensor.

P0037 – HO2S Heater Circuit Low (Bank 1 Sensor 2)

What it means: Downstream heater low.
Common causes: Sensor heater, wiring.
How urgent: Low.
What we do: Circuit test, sensor.

P0038 – HO2S Heater Circuit High (Bank 1 Sensor 2)

What it means: Downstream heater high.
Common causes: Sensor heater, wiring.
How urgent: Low.
What we do: Circuit test, sensor.

Catalytic converter codes

These are the expensive-sounding ones. The code only means the converter looks inefficient to the computer; it does not prove the converter is dead.

P0420 – Catalyst System Efficiency Below Threshold (Bank 1)

What it means: The converter on bank 1 isn’t cleaning the exhaust as well as it should, according to the O2 sensors.
Common causes: Worn-out converter, but very often: exhaust leak, lazy downstream O2 sensor, misfire or rich mixture that damaged the converter, wrong/aftermarket converter.
How urgent: Medium (fails NJ inspection).
What we do: We do NOT start with a converter. We check for exhaust leaks, test both O2 sensors, look for misfires and rich codes, and read converter temperatures. If the converter really is finished we show you the data and quote OEM-quality parts at an independent-shop price.

P0430 – Catalyst System Efficiency Below Threshold (Bank 2)

What it means: Same as P0420 on bank 2.
Common causes: Same as P0420.
How urgent: Medium (fails NJ inspection).
What we do: Same process as P0420.

P0421 – Warm Up Catalyst Efficiency Below Threshold (Bank 1)

What it means: The converter isn’t working well enough during warm-up.
Common causes: Same as P0420.
How urgent: Medium.
What we do: Same process as P0420.

P0431 – Warm Up Catalyst Efficiency Below Threshold (Bank 2)

What it means: Bank 2 converter inefficient during warm-up.
Common causes: Same as P0420.
How urgent: Medium.
What we do: Same process as P0420.

P0422 – Main Catalyst Efficiency Below Threshold (Bank 1)

What it means: Main converter inefficient.
Common causes: Same as P0420.
How urgent: Medium.
What we do: Same process as P0420.

P0432 – Main Catalyst Efficiency Below Threshold (Bank 2)

What it means: Bank 2 main converter inefficient.
Common causes: Same as P0420.
How urgent: Medium.
What we do: Same process as P0420.

P2096 – Post Catalyst Fuel Trim Too Lean (Bank 1)

What it means: Downstream sensor says mixture lean.
Common causes: Exhaust leak, downstream O2 sensor, converter, vacuum leak.
How urgent: Medium.
What we do: Leak and sensor checks before the converter.

P2097 – Post Catalyst Fuel Trim Too Rich (Bank 1)

What it means: Downstream sensor says mixture rich.
Common causes: Downstream O2 sensor, injector leak, converter.
How urgent: Medium.
What we do: Sensor and fuel checks.

P2098 – Post Catalyst Fuel Trim Too Lean (Bank 2)

What it means: Bank 2 post-cat lean.
Common causes: Same as P2096.
How urgent: Medium.
What we do: Same as P2096.

P2099 – Post Catalyst Fuel Trim Too Rich (Bank 2)

What it means: Bank 2 post-cat rich.
Common causes: Same as P2097.
How urgent: Medium.
What we do: Same as P2097.

EVAP (fuel vapor) codes

The EVAP system keeps gas fumes from escaping the tank. Leaks here are usually cheap: a gas cap, a cracked hose or a stuck valve.

P0440 – EVAP System Malfunction

What it means: General fuel-vapor system fault.
Common causes: Loose/worn gas cap, cracked hose, purge or vent valve, leaking tank seal.
How urgent: Low (fails inspection).
What we do: Gas cap first, then a smoke test of the EVAP system to find the leak.

P0441 – EVAP Incorrect Purge Flow

What it means: The purge valve isn’t letting vapor flow the way the computer expects.
Common causes: Stuck or failed purge valve, blocked hose, wiring.
How urgent: Low.
What we do: Purge valve test and replacement; a common cheap fix on Toyota, Honda, Hyundai/Kia and GM.

P0442 – EVAP Small Leak Detected

What it means: A small vapor leak.
Common causes: Gas cap, small cracked hose, aged seals, purge/vent valve not sealing.
How urgent: Low (fails inspection).
What we do: Cap, then smoke test. The leak is often a $20 hose.

P0443 – EVAP Purge Control Valve Circuit

What it means: Electrical fault in the purge valve circuit.
Common causes: Purge valve coil, connector, wiring.
How urgent: Low.
What we do: Circuit test, then valve.

P0446 – EVAP Vent Control Circuit

What it means: Vent valve circuit or valve stuck.
Common causes: Vent valve (often clogged with dirt near the tank), wiring.
How urgent: Low.
What we do: Vent valve test and replacement.

P0449 – EVAP Vent Valve/Solenoid Circuit

What it means: Electrical fault at the vent solenoid.
Common causes: Vent solenoid, wiring.
How urgent: Low.
What we do: Same as P0446. Very common on GM trucks and SUVs.

P0455 – EVAP Large Leak Detected

What it means: A big vapor leak.
Common causes: Gas cap missing or loose after a fill-up, cracked filler neck, disconnected hose, failed vent valve.
How urgent: Low (fails inspection).
What we do: Check the cap first. Tighten until it clicks and drive; if the light stays, smoke test.

P0456 – EVAP Very Small Leak Detected

What it means: A tiny leak.
Common causes: Gas cap seal, hairline hose crack, aged O-rings.
How urgent: Low.
What we do: Smoke test with a sensitive setup; a worn cap seal is the usual culprit.

P0457 – EVAP Leak Detected (Fuel Cap Loose/Off)

What it means: The computer thinks the cap is off.
Common causes: Gas cap not tightened after refueling, worn cap.
How urgent: Low.
What we do: Tighten or replace the cap; clear and drive.

P0496 – EVAP High Purge Flow

What it means: Vapor is flowing when it shouldn’t.
Common causes: Purge valve stuck open.
How urgent: Low.
What we do: Purge valve replacement. Very common on GM vehicles.

P0444 – EVAP Purge Control Valve Circuit Open

What it means: Purge valve circuit open.
Common causes: Valve, wiring, connector.
How urgent: Low.
What we do: Circuit test, valve.

P0445 – EVAP Purge Control Valve Circuit Shorted

What it means: Purge valve circuit shorted.
Common causes: Valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0447 – EVAP Vent Control Circuit Open

What it means: Vent circuit open.
Common causes: Vent valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0448 – EVAP Vent Control Circuit Shorted

What it means: Vent circuit shorted.
Common causes: Vent valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0450 – EVAP Pressure Sensor Malfunction

What it means: Tank pressure sensor fault.
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Sensor test.

P0451 – EVAP Pressure Sensor Range/Performance

What it means: Tank pressure reading off.
Common causes: Sensor, hose, wiring.
How urgent: Low.
What we do: Sensor and hose check.

P0452 – EVAP Pressure Sensor Low

What it means: Pressure sensor low.
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Circuit test, sensor.

P0453 – EVAP Pressure Sensor High

What it means: Pressure sensor high.
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Circuit test, sensor.

P0454 – EVAP Pressure Sensor Intermittent

What it means: Pressure sensor intermittent.
Common causes: Connector, wiring.
How urgent: Low.
What we do: Wiggle test.

P0458 – EVAP Purge Control Valve Circuit Low

What it means: Purge valve circuit low.
Common causes: Valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0459 – EVAP Purge Control Valve Circuit High

What it means: Purge valve circuit high.
Common causes: Valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0497 – EVAP Low Purge Flow

What it means: Not enough purge flow.
Common causes: Blocked purge line, valve stuck closed, canister.
How urgent: Low.
What we do: Purge valve and line test.

P0498 – EVAP Vent Valve Control Circuit Low

What it means: Vent control low.
Common causes: Vent valve, wiring.
How urgent: Low.
What we do: Circuit test.

P0499 – EVAP Vent Valve Control Circuit High

What it means: Vent control high.
Common causes: Vent valve, wiring.
How urgent: Low.
What we do: Circuit test.

P1450 – Unable to Bleed Up Fuel Tank Vacuum (Ford)

What it means: EVAP can’t release tank vacuum.
Common causes: Canister vent, purge valve stuck open, kinked hose.
How urgent: Low.
What we do: Purge and vent valve tests.

P0461 – Fuel Level Sensor Range/Performance

What it means: Fuel gauge sensor reading off.
Common causes: Sending unit, wiring.
How urgent: Low.
What we do: Sending unit test.

P0462 – Fuel Level Sensor Low Input

What it means: Fuel level signal low.
Common causes: Sending unit, wiring.
How urgent: Low.
What we do: Circuit test.

P0463 – Fuel Level Sensor High Input

What it means: Fuel level signal high.
Common causes: Sending unit, wiring.
How urgent: Low.
What we do: Circuit test.

EGR and emissions valve codes

Exhaust gas recirculation lowers combustion temperature. Carbon clogs it over time.

P0401 – EGR Flow Insufficient

What it means: Not enough exhaust is being recirculated.
Common causes: Carbon-clogged EGR valve or passages, failed valve, vacuum line, DPFE sensor on Fords.
How urgent: Low to medium.
What we do: Clean or replace the valve and clear the passages; test the sensor on Fords.

P0402 – EGR Flow Excessive

What it means: Too much exhaust recirculating.
Common causes: EGR valve stuck open, sensor fault.
How urgent: Medium (rough idle, stalling).
What we do: Valve cleaning/replacement.

P0404 – EGR Circuit Range/Performance

What it means: The EGR valve position doesn’t match the command.
Common causes: Sticking valve, position sensor, wiring.
How urgent: Low to medium.
What we do: Valve test, cleaning or replacement.

P0405 – EGR Sensor A Circuit Low

What it means: Position sensor reading low.
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Circuit test, then sensor/valve.

P0411 – Secondary Air Injection Incorrect Flow

What it means: Secondary air pump system isn’t working.
Common causes: Pump, check valve, relay, hose, fuse.
How urgent: Low (fails inspection).
What we do: Pump and valve test; often a relay, fuse or a rusted check valve.

P0403 – EGR Circuit Malfunction

What it means: EGR control circuit fault.
Common causes: EGR solenoid/valve, wiring.
How urgent: Low to medium.
What we do: Circuit test, valve.

P0406 – EGR Sensor A Circuit High

What it means: EGR position sensor high.
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Circuit test.

P0410 – Secondary Air Injection System Malfunction

What it means: Air pump system fault.
Common causes: Pump, relay, fuse, check valve.
How urgent: Low (fails inspection).
What we do: Pump/relay/valve tests.

P0412 – Secondary Air Injection Switching Valve A Circuit

What it means: Air switching valve circuit fault.
Common causes: Valve, solenoid, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0413 – Secondary Air Injection Switching Valve A Circuit Open

What it means: Air valve circuit open.
Common causes: Valve, wiring.
How urgent: Low.
What we do: Circuit test.

P0418 – Secondary Air Injection Relay A Circuit

What it means: Air pump relay fault.
Common causes: Relay, wiring, fuse.
How urgent: Low.
What we do: Relay/fuse test.

P0491 – Secondary Air Injection Insufficient Flow (Bank 1)

What it means: Not enough air pumped on bank 1.
Common causes: Pump, check valve, hose, carbon in passages.
How urgent: Low (fails inspection).
What we do: Flow test; passages are often clogged on Toyota/Lexus and VW.

P0492 – Secondary Air Injection Insufficient Flow (Bank 2)

What it means: Not enough air on bank 2.
Common causes: Same as P0491.
How urgent: Low.
What we do: Same as P0491.

Air intake, MAF, MAP and throttle codes

Sensors that measure the air coming into the engine. A dirty sensor or a vacuum leak confuses them.

P0100 – Mass Air Flow Circuit Malfunction

What it means: MAF sensor circuit fault.
Common causes: Dirty or failed MAF, connector, wiring, intake leak after the sensor.
How urgent: Medium.
What we do: Clean the MAF and check the intake boot before replacing the sensor.

P0101 – MAF Range/Performance

What it means: MAF reading doesn’t match engine load.
Common causes: Dirty MAF, intake leak, clogged air filter, aftermarket oiled filter residue.
How urgent: Medium.
What we do: MAF cleaning, intake leak check, air filter.

P0102 – MAF Circuit Low Input

What it means: MAF signal too low.
Common causes: Dirty/failed MAF, wiring, unplugged connector.
How urgent: Medium.
What we do: Connector and wiring check, then sensor.

P0105 – MAP Sensor Circuit

What it means: Manifold pressure sensor fault.
Common causes: Failed MAP sensor, vacuum hose, wiring.
How urgent: Medium.
What we do: Vacuum hose check, then sensor.

P0106 – MAP Range/Performance

What it means: MAP reading doesn’t make sense.
Common causes: Vacuum leak, failed sensor, exhaust restriction.
How urgent: Medium.
What we do: Leak test and sensor comparison.

P0107 – MAP Circuit Low Input

What it means: MAP signal low.
Common causes: Sensor, wiring, connector.
How urgent: Medium.
What we do: Circuit test, then sensor.

P0108 – MAP Circuit High Input

What it means: MAP signal high.
Common causes: Sensor, wiring, vacuum hose off.
How urgent: Medium.
What we do: Same as P0107.

P0110 – Intake Air Temperature Circuit

What it means: IAT sensor fault (often built into the MAF).
Common causes: Sensor, wiring.
How urgent: Low.
What we do: Circuit test; the sensor is cheap.

P0113 – Intake Air Temperature High Input

What it means: IAT reading open/high.
Common causes: Unplugged or failed sensor, wiring.
How urgent: Low.
What we do: Connector check, then sensor.

P0120 – Throttle Position Sensor Circuit

What it means: TPS or throttle body sensor fault.
Common causes: Failed TPS, dirty throttle body, wiring.
How urgent: Medium.
What we do: Throttle body cleaning and sensor test; relearn afterwards.

P0121 – Throttle Position Range/Performance

What it means: TPS reading doesn’t match.
Common causes: Worn TPS, carbon in throttle body.
How urgent: Medium.
What we do: Same as P0120.

P0122 – Throttle Position Sensor Low Input

What it means: TPS signal low.
Common causes: Sensor, wiring, connector.
How urgent: Medium.
What we do: Circuit test, then sensor.

P0123 – Throttle Position Sensor High Input

What it means: TPS signal high.
Common causes: Sensor, wiring.
How urgent: Medium.
What we do: Same as P0122.

P0507 – Idle Control System RPM Higher Than Expected

What it means: Engine idles too fast.
Common causes: Vacuum leak, dirty throttle body, idle air valve, throttle body needs relearn after cleaning or battery disconnect.
How urgent: Low to medium.
What we do: Leak test, throttle cleaning and an idle relearn with the scan tool.

P0505 – Idle Control System Malfunction

What it means: Idle control problem.
Common causes: Idle air control valve, throttle body, vacuum leak.
How urgent: Low to medium.
What we do: Clean/replace the valve, relearn.

P2111 – Throttle Actuator Control System Stuck Open

What it means: Electronic throttle stuck open.
Common causes: Failed throttle body, debris, wiring.
How urgent: High.
What we do: Throttle body test and replacement; the car may go into limp mode.

P2112 – Throttle Actuator Control System Stuck Closed

What it means: Electronic throttle stuck closed.
Common causes: Failed throttle body, carbon, wiring.
How urgent: High.
What we do: Same as P2111.

P2135 – Throttle/Pedal Position Sensor Correlation

What it means: The two throttle sensors disagree.
Common causes: Throttle body sensor, pedal sensor, wiring, corroded connector.
How urgent: High (limp mode).
What we do: Live-data comparison of both sensors, connector inspection, then throttle body or pedal.

P2138 – Throttle/Pedal Position Sensor D/E Correlation

What it means: Pedal position sensors disagree.
Common causes: Accelerator pedal sensor, wiring.
How urgent: High (limp mode).
What we do: Pedal assembly test and replacement.

P0068 – MAP/MAF – Throttle Position Correlation

What it means: Airflow sensors disagree with the throttle.
Common causes: Big vacuum leak, intake boot off, MAF/MAP fault, throttle body.
How urgent: Medium to high.
What we do: Intake inspection and leak test; often a popped intake hose.

P0069 – MAP/Barometric Pressure Correlation

What it means: MAP and baro readings disagree.
Common causes: MAP sensor, vacuum leak, wiring.
How urgent: Medium.
What we do: Sensor comparison.

P0111 – Intake Air Temperature Range/Performance

What it means: IAT reading doesn’t track.
Common causes: Sensor, wiring, dirty MAF.
How urgent: Low.
What we do: Sensor test.

P0112 – Intake Air Temperature Low Input

What it means: IAT signal low.
Common causes: Sensor short, wiring.
How urgent: Low.
What we do: Circuit test, sensor.

P0299 – Turbo/Supercharger Underboost

What it means: Boost pressure lower than commanded.
Common causes: Boost leak (hose, intercooler), wastegate/diverter valve, boost solenoid, turbo wear, clogged air filter.
How urgent: Medium (limp mode).
What we do: Boost leak test, wastegate/diverter valve test. Very common on Audi/VW, BMW, Ford EcoBoost, Hyundai/Kia turbo engines.

P0234 – Turbo/Supercharger Overboost

What it means: Boost higher than commanded.
Common causes: Wastegate stuck closed, boost solenoid, vacuum lines.
How urgent: Medium to high.
What we do: Wastegate and control tests.

P0236 – Turbo Boost Sensor Range/Performance

What it means: Boost sensor reading off.
Common causes: Sensor, leak, wiring.
How urgent: Medium.
What we do: Sensor comparison and leak test.

P2263 – Turbo/Supercharger Boost System Performance

What it means: Boost system not performing.
Common causes: Leak, wastegate actuator, turbo, carbon in VNT vanes (diesel).
How urgent: Medium.
What we do: Boost leak and actuator tests.

P0243 – Turbo Wastegate Solenoid A Circuit

What it means: Wastegate solenoid circuit fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Circuit test, solenoid.

P0245 – Turbo Wastegate Solenoid A Low

What it means: Wastegate solenoid low.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Circuit test.

P0103 – MAF Circuit High Input

What it means: MAF signal too high.
Common causes: Failed MAF, wiring short.
How urgent: Medium.
What we do: Circuit test, sensor.

P0104 – MAF Circuit Intermittent

What it means: MAF signal drops out.
Common causes: Connector, wiring, failing sensor.
How urgent: Medium.
What we do: Wiggle test and connector repair.

P0222 – Throttle Position Sensor B Low Input

What it means: Second throttle sensor low.
Common causes: Throttle body sensor, wiring.
How urgent: High (limp mode).
What we do: Circuit test, throttle body.

P0223 – Throttle Position Sensor B High Input

What it means: Second throttle sensor high.
Common causes: Throttle body sensor, wiring.
How urgent: High.
What we do: Same as P0222.

P2119 – Throttle Actuator Control Throttle Body Range/Performance

What it means: Throttle body not responding correctly.
Common causes: Carbon, worn throttle body motor/gears, wiring.
How urgent: Medium to high.
What we do: Cleaning and relearn first, then throttle body.

P2101 – Throttle Actuator Control Motor Circuit Range/Performance

What it means: Throttle motor circuit fault.
Common causes: Throttle body motor, wiring, ECU driver.
How urgent: High.
What we do: Circuit test, throttle body.

P0506 – Idle Control System RPM Lower Than Expected

What it means: Idle too low.
Common causes: Dirty throttle body, idle valve, vacuum leak, carbon.
How urgent: Low to medium.
What we do: Throttle cleaning and relearn.

P0508 – Idle Air Control Circuit Low

What it means: IAC circuit low.
Common causes: IAC valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0509 – Idle Air Control Circuit High

What it means: IAC circuit high.
Common causes: IAC valve, wiring.
How urgent: Low.
What we do: Circuit test, valve.

P0510 – Closed Throttle Position Switch

What it means: Idle switch fault.
Common causes: TPS, wiring.
How urgent: Low.
What we do: Sensor test.

Engine temperature and cooling codes

A thermostat or temperature sensor problem. These also hurt fuel economy and can fail inspection.

P0115 – Engine Coolant Temperature Circuit

What it means: Coolant temp sensor circuit fault.
Common causes: Sensor, wiring, connector.
How urgent: Medium.
What we do: Circuit test, then sensor.

P0116 – Coolant Temperature Range/Performance

What it means: Temp reading doesn’t track warm-up.
Common causes: Sensor, thermostat stuck open, low coolant.
How urgent: Medium.
What we do: Thermostat and sensor check, coolant level.

P0117 – Coolant Temperature Low Input

What it means: Sensor reads too hot/short.
Common causes: Sensor, wiring short.
How urgent: Medium.
What we do: Circuit test, then sensor.

P0118 – Coolant Temperature High Input

What it means: Sensor reads open/cold.
Common causes: Sensor, unplugged connector, wiring.
How urgent: Medium.
What we do: Connector check, then sensor.

P0125 – Insufficient Coolant Temperature for Closed Loop

What it means: Engine never gets warm enough.
Common causes: Thermostat stuck open, low coolant, sensor.
How urgent: Medium (fails inspection, poor MPG).
What we do: Thermostat replacement is the usual fix.

P0128 – Coolant Thermostat Below Regulating Temperature

What it means: Engine warms up too slowly.
Common causes: Thermostat stuck open (most common), low coolant, cooling fan stuck on, sensor.
How urgent: Medium (fails inspection).
What we do: Thermostat replacement; very common on GM, Chrysler/Jeep, Honda and VW.

P0217 – Engine Over Temperature

What it means: Engine overheated.
Common causes: Low coolant, fan failure, thermostat stuck closed, water pump, head gasket.
How urgent: High (stop driving).
What we do: Pressure test, fan and thermostat test, water pump check. Do not keep driving an overheating engine.

P0480 – Cooling Fan 1 Control Circuit

What it means: Cooling fan circuit fault.
Common causes: Fan relay, fan motor, wiring, fuse.
How urgent: Medium.
What we do: Relay/fuse/motor test.

P0119 – Coolant Temperature Sensor Intermittent

What it means: Temp sensor signal intermittent.
Common causes: Connector, wiring, sensor.
How urgent: Medium.
What we do: Wiggle test, connector.

P0597 – Thermostat Heater Control Circuit Open

What it means: Electronic thermostat circuit open.
Common causes: Map-controlled thermostat (common on BMW, VW/Audi, GM), wiring.
How urgent: Medium.
What we do: Circuit test, thermostat replacement.

P0598 – Thermostat Heater Control Circuit Low

What it means: Electronic thermostat circuit low.
Common causes: Thermostat, wiring.
How urgent: Medium.
What we do: Same as P0597.

P0599 – Thermostat Heater Control Circuit High

What it means: Electronic thermostat circuit high.
Common causes: Thermostat, wiring.
How urgent: Medium.
What we do: Same as P0597.

P0481 – Cooling Fan 2 Control Circuit

What it means: Second fan circuit fault.
Common causes: Relay, motor, wiring.
How urgent: Medium.
What we do: Relay/motor test.

P0483 – Cooling Fan Rationality Check

What it means: Fan not performing as expected.
Common causes: Fan motor/module, relay, wiring.
How urgent: Medium.
What we do: Fan module and motor test.

P0526 – Fan Speed Sensor Circuit

What it means: Fan speed signal missing.
Common causes: Fan module, wiring.
How urgent: Medium.
What we do: Module and circuit test.

P1299 – Cylinder Head Over Temperature Protection (Ford)

What it means: Engine overheated; power reduced to protect it.
Common causes: Low coolant, fan, thermostat, water pump, head gasket.
How urgent: High.
What we do: Cooling system pressure test; do not drive hot.

Ignition and cam/crank sensor codes

Timing and spark. Some of these will leave you stranded; a few are a quick sensor swap.

P0335 – Crankshaft Position Sensor Circuit

What it means: The computer isn’t getting a clean crank signal.
Common causes: Failed crank sensor, wiring, damaged reluctor ring, timing belt/chain issue.
How urgent: High (no-start or stalling).
What we do: Sensor and wiring test; confirm timing. A failing crank sensor often stalls when hot and restarts when cool.

P0336 – Crankshaft Position Sensor Range/Performance

What it means: Crank signal is erratic.
Common causes: Sensor, damaged tone ring, debris, wiring.
How urgent: High.
What we do: Same as P0335.

P0340 – Camshaft Position Sensor Circuit

What it means: Cam sensor fault.
Common causes: Cam sensor, wiring, timing chain stretch, oil contamination.
How urgent: High (may not start).
What we do: Sensor and wiring test; check cam/crank correlation for timing chain wear.

P0341 – Camshaft Position Sensor Range/Performance

What it means: Cam signal out of range.
Common causes: Sensor, stretched timing chain, VVT fault, low oil.
How urgent: Medium to high.
What we do: Correlation check with the scan tool; chain wear is common on some BMW, Audi/VW, Nissan and GM engines.

P0345 – Camshaft Position Sensor Circuit (Bank 2)

What it means: Cam sensor fault on bank 2.
Common causes: Same as P0340.
How urgent: High.
What we do: Same as P0340.

P0350 – Ignition Coil Primary/Secondary Circuit

What it means: General coil circuit fault.
Common causes: Failed coil, wiring, connector, ECU driver.
How urgent: Medium to high.
What we do: Coil test; swap to confirm.

P0351 – Ignition Coil A Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 1 (P0352–P0358 are cylinders 2–8).
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Coil swap test, then replacement.

P0016 – Crankshaft/Camshaft Position Correlation (Bank 1 Sensor A)

What it means: Cam and crank timing don’t line up.
Common causes: Stretched timing chain, jumped belt, VVT actuator stuck, low oil, failed sensor.
How urgent: High.
What we do: Live correlation check. On high-mileage engines this is often the timing chain; on others a VVT solenoid or oil issue.

P0017 – Crankshaft/Camshaft Position Correlation (Bank 1 Sensor B)

What it means: Exhaust cam/crank correlation fault.
Common causes: Same as P0016.
How urgent: High.
What we do: Same as P0016.

P0018 – Crankshaft/Camshaft Position Correlation (Bank 2 Sensor A)

What it means: Bank 2 correlation fault.
Common causes: Same as P0016.
How urgent: High.
What we do: Same as P0016.

P0352 – Ignition Coil B Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 2.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 2 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0353 – Ignition Coil C Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 3.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 3 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0354 – Ignition Coil D Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 4.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 4 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0355 – Ignition Coil E Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 5.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 5 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0356 – Ignition Coil F Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 6.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 6 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0357 – Ignition Coil G Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 7.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 7 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0358 – Ignition Coil H Primary/Secondary Circuit

What it means: Coil circuit fault on cylinder 8.
Common causes: Coil, connector, wiring.
How urgent: Medium to high.
What we do: Swap the cylinder 8 coil with a neighbor and re-scan; if the code follows, replace the coil.

P0316 – Misfire Detected on Startup (First 1000 Revolutions)

What it means: Misfire right after start.
Common causes: Plugs, coils, injectors, low compression, cam/crank sensor.
How urgent: Medium.
What we do: Cold-start misfire data and cylinder tests.

P0313 – Misfire Detected With Low Fuel

What it means: Misfire when the tank is low.
Common causes: Running out of fuel, weak fuel pump, pickup.
How urgent: Low to medium.
What we do: Fuel level and pump test.

P0320 – Ignition/Distributor Engine Speed Input Circuit

What it means: Engine speed signal fault.
Common causes: Crank sensor, wiring, ignition module.
How urgent: High.
What we do: Sensor and circuit test.

P0339 – Crankshaft Position Sensor Circuit Intermittent

What it means: Crank signal drops out.
Common causes: Sensor, connector, wiring, reluctor.
How urgent: High.
What we do: Sensor and wiring test.

P0343 – Camshaft Position Sensor High Input

What it means: Cam sensor signal high.
Common causes: Sensor, wiring.
How urgent: High.
What we do: Sensor and circuit test.

P0344 – Camshaft Position Sensor Intermittent

What it means: Cam signal intermittent.
Common causes: Sensor, connector, wiring.
How urgent: High.
What we do: Sensor and wiring test.

P0019 – Crankshaft/Camshaft Position Correlation (Bank 2 Sensor B)

What it means: Bank 2 exhaust cam correlation fault.
Common causes: Timing chain, VVT, oil, sensor.
How urgent: High.
What we do: Correlation check with scan tool.

P0008 – Engine Position System Performance (Bank 1)

What it means: Crank and cam positions out of sync.
Common causes: Stretched timing chain (very common on some GM V6 and Ford engines), VVT.
How urgent: High.
What we do: Timing chain inspection.

P0009 – Engine Position System Performance (Bank 2)

What it means: Bank 2 timing out of sync.
Common causes: Timing chain, VVT.
How urgent: High.
What we do: Timing chain inspection.

Variable valve timing (VVT) codes

Common on modern engines. Very often an oil-level, oil-quality or solenoid problem rather than a mechanical one.

P0010 – Camshaft Position Actuator Circuit (Bank 1)

What it means: VVT actuator/solenoid circuit fault.
Common causes: VVT solenoid, wiring, connector.
How urgent: Medium.
What we do: Solenoid test and replacement; check oil level and condition.

P0011 – Camshaft Position Timing Over-Advanced (Bank 1)

What it means: Intake cam timing is too far advanced or stuck.
Common causes: Low or dirty oil, clogged VVT solenoid screen, failed solenoid, worn phaser, timing chain.
How urgent: Medium.
What we do: Oil change if overdue, solenoid cleaning/replacement, then phaser/chain inspection. Very common on Hyundai/Kia, Nissan, GM Ecotec, Toyota and VW.

P0012 – Camshaft Position Timing Over-Retarded (Bank 1)

What it means: Intake cam timing is too far retarded.
Common causes: Same as P0011.
How urgent: Medium.
What we do: Same as P0011.

P0013 – Exhaust Cam Actuator Circuit (Bank 1)

What it means: Exhaust VVT solenoid circuit fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Solenoid test and replacement.

P0014 – Exhaust Cam Timing Over-Advanced (Bank 1)

What it means: Exhaust cam timing out of range.
Common causes: Oil, solenoid, phaser, chain.
How urgent: Medium.
What we do: Same as P0011.

P0020 – Camshaft Position Actuator Circuit (Bank 2)

What it means: Bank 2 VVT circuit fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Same as P0010.

P0021 – Camshaft Position Timing Over-Advanced (Bank 2)

What it means: Bank 2 cam timing out of range.
Common causes: Same as P0011.
How urgent: Medium.
What we do: Same as P0011.

P0024 – Exhaust Cam Timing Over-Advanced (Bank 2)

What it means: Bank 2 exhaust cam timing out of range.
Common causes: Same as P0011.
How urgent: Medium.
What we do: Same as P0011.

P0015 – Exhaust Cam Timing Over-Retarded (Bank 1)

What it means: Exhaust cam timing retarded.
Common causes: Oil, solenoid, phaser, chain.
How urgent: Medium.
What we do: Same as P0011.

P0022 – Camshaft Position Timing Over-Retarded (Bank 2)

What it means: Bank 2 intake cam retarded.
Common causes: Oil, solenoid, phaser, chain.
How urgent: Medium.
What we do: Same as P0011.

P0025 – Exhaust Cam Timing Over-Retarded (Bank 2)

What it means: Bank 2 exhaust cam retarded.
Common causes: Oil, solenoid, phaser, chain.
How urgent: Medium.
What we do: Same as P0011.

P0023 – Exhaust Cam Actuator Circuit (Bank 2)

What it means: Bank 2 exhaust VVT circuit fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Solenoid test.

P0026 – Intake Valve Control Solenoid Range/Performance (Bank 1)

What it means: VVT solenoid not performing.
Common causes: Solenoid, oil, screen clogged.
How urgent: Medium.
What we do: Solenoid cleaning/replacement, oil change.

P0028 – Intake Valve Control Solenoid Range/Performance (Bank 2)

What it means: Bank 2 VVT solenoid not performing.
Common causes: Solenoid, oil.
How urgent: Medium.
What we do: Same as P0026.

P000A – Camshaft Position Slow Response (Bank 1)

What it means: Cam phaser responds slowly.
Common causes: Oil condition, solenoid, phaser.
How urgent: Medium.
What we do: Oil service and solenoid test.

P000B – Camshaft Position Slow Response (Bank 1 Exhaust)

What it means: Exhaust cam phaser slow.
Common causes: Oil, solenoid, phaser.
How urgent: Medium.
What we do: Same as P000A.

Transmission codes (P07xx, P08xx)

The transmission control module watches gear ratios, solenoids, sensors and fluid temperature. Fluid condition is the first thing we check.

P0700 – Transmission Control System Malfunction

What it means: The transmission computer has stored a fault; this code just turns on the light. The real code is in the transmission module.
Common causes: Any transmission fault.
How urgent: Medium.
What we do: We read the transmission module directly to find the actual code, then diagnose that.

P0705 – Transmission Range Sensor Circuit (PRNDL)

What it means: The computer can’t tell what gear you selected.
Common causes: Range/neutral safety switch, misadjusted linkage, wiring.
How urgent: Medium (may not start in Park).
What we do: Switch adjustment or replacement.

P0710 – Transmission Fluid Temperature Sensor Circuit

What it means: Fluid temp sensor fault.
Common causes: Sensor (often inside the valve body), wiring.
How urgent: Low to medium.
What we do: Circuit test; sensor replacement.

P0715 – Input/Turbine Speed Sensor Circuit

What it means: Input speed sensor fault.
Common causes: Sensor, wiring, debris on the sensor.
How urgent: Medium (harsh shifts, limp mode).
What we do: Sensor test and replacement; fluid check.

P0720 – Output Speed Sensor Circuit

What it means: Output speed sensor fault.
Common causes: Sensor, wiring.
How urgent: Medium.
What we do: Sensor test and replacement.

P0730 – Incorrect Gear Ratio

What it means: The transmission isn’t producing the gear ratio commanded.
Common causes: Low or burnt fluid, worn clutches, valve body, solenoid.
How urgent: Medium to high.
What we do: Fluid check first, then solenoid/valve body tests. We tell you honestly whether it’s a fluid service, a valve body, or time to talk about a rebuild.

P0731 – Gear 1 Incorrect Ratio

What it means: Slipping in 1st gear (P0732–P0736 are gears 2–6).
Common causes: Same as P0730.
How urgent: Medium to high.
What we do: Same as P0730.

P0732 – Gear 2 Incorrect Ratio

What it means: Slipping in 2nd gear.
Common causes: Same as P0730.
How urgent: Medium to high.
What we do: Same as P0730.

P0733 – Gear 3 Incorrect Ratio

What it means: Slipping in 3rd gear.
Common causes: Same as P0730.
How urgent: Medium to high.
What we do: Same as P0730.

P0734 – Gear 4 Incorrect Ratio

What it means: Slipping in 4th gear.
Common causes: Same as P0730.
How urgent: Medium to high.
What we do: Same as P0730.

P0740 – Torque Converter Clutch Circuit

What it means: Lock-up clutch circuit fault.
Common causes: TCC solenoid, wiring, valve body.
How urgent: Medium.
What we do: Solenoid and circuit test.

P0741 – Torque Converter Clutch Stuck Off / Performance

What it means: The converter clutch isn’t locking up.
Common causes: Worn converter clutch, TCC solenoid, low/burnt fluid, valve body.
How urgent: Medium (worse MPG, shudder).
What we do: Fluid condition, solenoid test, converter lock-up test on a road test.

P0742 – Torque Converter Clutch Stuck On

What it means: Converter clutch won’t release.
Common causes: Solenoid stuck, valve body.
How urgent: Medium to high (stalls when stopping).
What we do: Solenoid/valve body test.

P0750 – Shift Solenoid A Malfunction

What it means: Shift solenoid A fault (P0755 = B, P0760 = C, P0765 = D).
Common causes: Solenoid, wiring, valve body, dirty fluid.
How urgent: Medium.
What we do: Solenoid resistance/command test; often replaceable without pulling the transmission.

P0751 – Shift Solenoid A Performance / Stuck Off

What it means: Solenoid A isn’t shifting the gear.
Common causes: Sticking solenoid, debris, valve body, fluid.
How urgent: Medium.
What we do: Fluid service plus solenoid replacement in most cases.

P0755 – Shift Solenoid B Malfunction

What it means: Solenoid B fault.
Common causes: Same as P0750.
How urgent: Medium.
What we do: Same as P0750.

P0756 – Shift Solenoid B Performance / Stuck Off

What it means: Solenoid B not shifting.
Common causes: Same as P0751.
How urgent: Medium.
What we do: Same as P0751.

P0776 – Pressure Control Solenoid B Performance

What it means: Line pressure solenoid out of range.
Common causes: Solenoid, valve body, fluid.
How urgent: Medium.
What we do: Solenoid and pressure testing.

P0841 – Transmission Fluid Pressure Sensor Range/Performance

What it means: Pressure sensor reading off.
Common causes: Sensor, low fluid, valve body.
How urgent: Medium.
What we do: Fluid level/condition first, then sensor.

P0868 – Transmission Fluid Pressure Low

What it means: Line pressure is low.
Common causes: Low fluid, worn pump, pressure solenoid, internal leak.
How urgent: Medium to high.
What we do: Fluid check, pressure test, honest assessment.

P0894 – Transmission Component Slipping

What it means: The transmission is slipping.
Common causes: Low/burnt fluid, worn clutches, solenoids.
How urgent: High.
What we do: Same as P0730. If it’s slipping badly we’ll tell you straight whether a repair makes sense for the car’s value.

P0735 – Gear 5 Incorrect Ratio

What it means: Slipping in 5th gear.
Common causes: Low or burnt fluid, worn clutches, valve body, solenoid.
How urgent: Medium to high.
What we do: Fluid check first, then solenoid/valve body tests; honest assessment before any rebuild talk.

P0736 – Gear 6 Incorrect Ratio

What it means: Slipping in 6th gear.
Common causes: Low or burnt fluid, worn clutches, valve body, solenoid.
How urgent: Medium to high.
What we do: Fluid check first, then solenoid/valve body tests; honest assessment before any rebuild talk.

P0760 – Shift Solenoid C Malfunction

What it means: Transmission solenoid fault.
Common causes: Sticking or failed solenoid, dirty/burnt fluid, wiring, valve body.
How urgent: Medium.
What we do: Fluid condition, solenoid resistance and command tests; many solenoids are replaceable without removing the transmission.

P0761 – Shift Solenoid C Performance / Stuck Off

P0765 – Shift Solenoid D Malfunction

P0766 – Shift Solenoid D Performance / Stuck Off

P0770 – Shift Solenoid E Malfunction

P0771 – Shift Solenoid E Performance / Stuck Off

P0745 – Pressure Control Solenoid A Malfunction

P0746 – Pressure Control Solenoid A Performance / Stuck Off

P0748 – Pressure Control Solenoid A Electrical

P0753 – Shift Solenoid A Electrical

P0758 – Shift Solenoid B Electrical

P0763 – Shift Solenoid C Electrical

P0768 – Shift Solenoid D Electrical

P0773 – Shift Solenoid E Electrical

P0711 – Transmission Fluid Temperature Sensor Range/Performance

What it means: Fluid temp reading doesn’t track.
Common causes: Sensor, wiring, actual overheating.
How urgent: Medium.
What we do: Sensor test; check for transmission overheating.

P0712 – Transmission Fluid Temperature Sensor Low

What it means: Temp sensor signal low.
Common causes: Sensor, wiring short.
How urgent: Low to medium.
What we do: Circuit test, sensor.

P0713 – Transmission Fluid Temperature Sensor High

What it means: Temp sensor signal high/open.
Common causes: Sensor, connector, wiring.
How urgent: Low to medium.
What we do: Circuit test, sensor.

P0716 – Input/Turbine Speed Sensor Range/Performance

What it means: Input speed signal erratic.
Common causes: Sensor, debris, wiring.
How urgent: Medium.
What we do: Sensor test and replacement.

P0717 – Input/Turbine Speed Sensor No Signal

What it means: No input speed signal.
Common causes: Sensor, wiring, connector.
How urgent: Medium (limp mode).
What we do: Sensor and wiring test.

P0721 – Output Speed Sensor Range/Performance

What it means: Output speed erratic.
Common causes: Sensor, debris, wiring.
How urgent: Medium.
What we do: Sensor test.

P0722 – Output Speed Sensor No Signal

What it means: No output speed signal.
Common causes: Sensor, wiring.
How urgent: Medium (speedometer/shift issues).
What we do: Sensor and wiring test.

P0729 – Gear 6 Incorrect Ratio

What it means: Slipping in 6th gear.
Common causes: Fluid, clutches, valve body.
How urgent: Medium to high.
What we do: Same as P0730.

P0743 – Torque Converter Clutch Circuit Electrical

What it means: TCC solenoid electrical fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Circuit and solenoid test.

P0744 – Torque Converter Clutch Circuit Intermittent

What it means: Intermittent TCC fault.
Common causes: Wiring, connector, solenoid.
How urgent: Medium.
What we do: Wiggle test, connector inspection.

P0780 – Shift Malfunction

What it means: General shift fault.
Common causes: Fluid, solenoids, valve body.
How urgent: Medium.
What we do: Full transmission module scan and fluid check.

P0781 – 1-2 Shift Malfunction

What it means: Problem shifting 1st to 2nd.
Common causes: Solenoid, valve body, fluid.
How urgent: Medium.
What we do: Solenoid/valve body tests.

P0782 – 2-3 Shift Malfunction

What it means: Problem shifting 2nd to 3rd.
Common causes: Solenoid, valve body, fluid.
How urgent: Medium.
What we do: Same as P0781.

P0783 – 3-4 Shift Malfunction

What it means: Problem shifting 3rd to 4th.
Common causes: Solenoid, valve body, fluid.
How urgent: Medium.
What we do: Same as P0781.

P0842 – Transmission Fluid Pressure Sensor Low

What it means: Pressure sensor signal low.
Common causes: Sensor, wiring, low fluid.
How urgent: Medium.
What we do: Fluid level, then sensor.

P0843 – Transmission Fluid Pressure Sensor High

What it means: Pressure sensor signal high.
Common causes: Sensor, wiring.
How urgent: Medium.
What we do: Circuit test, sensor.

P0882 – TCM Power Input Signal Low

What it means: Transmission module losing power.
Common causes: Fuse, relay, wiring, low battery.
How urgent: Medium to high.
What we do: Power and ground checks.

P0218 – Transmission Fluid Over Temperature

What it means: Transmission overheated.
Common causes: Low fluid, towing/heavy load, cooler blocked, slipping clutches.
How urgent: High.
What we do: Fluid check, cooler flow test, cause of heat.

P2714 – Pressure Control Solenoid D Performance / Stuck Off

What it means: Solenoid D not responding.
Common causes: Solenoid, fluid, valve body.
How urgent: Medium.
What we do: Solenoid and fluid tests (common on Toyota/Lexus).

P2716 – Pressure Control Solenoid D Electrical

What it means: Solenoid D circuit fault.
Common causes: Solenoid, wiring.
How urgent: Medium.
What we do: Circuit test, solenoid.

P0219 – Engine Overspeed

What it means: Engine RPM exceeded limit.
Common causes: Downshift error, driver, transmission slip.
How urgent: Low.
What we do: Usually informational; we check the transmission for slip.

Other common engine and body codes

Knock sensors, idle control, injectors, purge valves, battery/charging and a few network codes.

P0325 – Knock Sensor 1 Circuit

What it means: Knock sensor fault.
Common causes: Failed knock sensor, wiring (often corroded), loose sensor.
How urgent: Low to medium (reduced power/MPG).
What we do: Circuit test, then sensor. Common on Nissan, Toyota and GM.

P0327 – Knock Sensor 1 Circuit Low Input

What it means: Knock sensor signal low.
Common causes: Sensor, wiring.
How urgent: Low to medium.
What we do: Same as P0325.

P0332 – Knock Sensor 2 Circuit Low Input

What it means: Bank 2 knock sensor low.
Common causes: Sensor, wiring.
How urgent: Low to medium.
What we do: Same as P0325.

P0562 – System Voltage Low

What it means: Battery/charging voltage too low.
Common causes: Weak battery, failing alternator, corroded terminals or ground.
How urgent: Medium (may strand you).
What we do: Battery and charging test; clean terminals; alternator if needed.

P0563 – System Voltage High

What it means: Charging voltage too high.
Common causes: Failed voltage regulator/alternator.
How urgent: Medium (can damage electronics).
What we do: Alternator test and replacement.

P0600 – Serial Communication Link

What it means: Modules aren’t talking to each other.
Common causes: Wiring, connectors, a failing module, low battery voltage.
How urgent: Medium.
What we do: Network scan and wiring check; low voltage causes many of these.

P0601 – Internal Control Module Memory Checksum Error

What it means: The ECU has an internal memory fault.
Common causes: ECU failure, bad reprogramming, voltage spike.
How urgent: Medium to high.
What we do: Try a reflash with factory software first; replace and program the module only if needed.

P0606 – ECM/PCM Processor Fault

What it means: The engine computer has an internal processor fault.
Common causes: ECU, power/ground problems.
How urgent: Medium to high.
What we do: Power and ground checks before condemning the module; module programming if replaced.

P0627 – Fuel Pump A Control Circuit Open

What it means: Fuel pump control circuit open.
Common causes: Fuel pump relay/driver module, wiring, pump.
How urgent: High (no-start).
What we do: Relay/module and wiring test.

P0685 – ECM/PCM Power Relay Control Circuit

What it means: Main relay circuit fault.
Common causes: Main relay, wiring, fuse.
How urgent: Medium.
What we do: Relay and circuit test.

P1000 – OBD Systems Readiness Test Not Complete (Ford)

What it means: The car hasn’t finished its self-tests after a battery disconnect or code clear.
Common causes: Not a fault; monitors not yet run.
How urgent: None (but fails inspection as ‘not ready’).
What we do: Drive cycle; we check readiness and explain the drive pattern.

P2187 – System Too Lean at Idle (Bank 1)

What it means: Lean only at idle.
Common causes: Vacuum leak, PCV valve/hose, intake gasket.
How urgent: Medium.
What we do: Smoke test; very often a PCV hose or intake boot on Audi/VW and GM.

P2177 – System Too Lean Off Idle (Bank 1)

What it means: Lean under load.
Common causes: MAF, fuel delivery, exhaust leak.
How urgent: Medium.
What we do: Fuel pressure and MAF tests.

U0100 – Lost Communication With ECM/PCM

What it means: Another module can’t talk to the engine computer.
Common causes: Wiring/connector, blown fuse, low battery, ECU power/ground, failed ECU.
How urgent: High (may not start).
What we do: Network and power checks first; most U0100s are a connector or voltage problem, not a dead computer.

U0101 – Lost Communication With TCM

What it means: Can’t talk to the transmission module.
Common causes: Wiring, fuse, TCM power/ground, failed TCM.
How urgent: High.
What we do: Same approach as U0100.

U0121 – Lost Communication With ABS Module

What it means: Can’t talk to the ABS module.
Common causes: Wiring, fuse, ABS module.
How urgent: Medium to high.
What we do: Same approach as U0100.

U0155 – Lost Communication With Instrument Cluster

What it means: Can’t talk to the dashboard cluster.
Common causes: Wiring, fuse, cluster.
How urgent: Medium.
What we do: Same approach as U0100.

B1000 – Body Control Module Fault (manufacturer-specific)

What it means: Generic body-module code; meaning varies by make.
Common causes: Varies.
How urgent: Varies.
What we do: We read the manufacturer-specific definition with factory-level software.

P0328 – Knock Sensor 1 Circuit High Input

What it means: Knock sensor signal high.
Common causes: Sensor, wiring.
How urgent: Low to medium.
What we do: Circuit test, sensor.

P0330 – Knock Sensor 2 Circuit

What it means: Bank 2 knock sensor fault.
Common causes: Sensor, wiring.
How urgent: Low to medium.
What we do: Same as P0325.

P0333 – Knock Sensor 2 Circuit High Input

What it means: Bank 2 knock sensor high.
Common causes: Sensor, wiring.
How urgent: Low to medium.
What we do: Same as P0325.

P0560 – System Voltage Malfunction

What it means: Voltage out of range.
Common causes: Battery, alternator, terminals, grounds.
How urgent: Medium.
What we do: Battery/charging test.

P0620 – Generator Control Circuit

What it means: Alternator control circuit fault.
Common causes: Alternator, wiring, ECU.
How urgent: Medium.
What we do: Charging test.

P0621 – Generator Lamp L Terminal Circuit

What it means: Alternator lamp circuit fault.
Common causes: Alternator, wiring.
How urgent: Low to medium.
What we do: Charging test.

P0622 – Generator Field F Terminal Circuit

What it means: Alternator field circuit fault.
Common causes: Alternator, wiring.
How urgent: Medium.
What we do: Charging test, alternator.

P0602 – Control Module Programming Error

What it means: The module has a programming fault or was never programmed.
Common causes: Failed flash, replaced module not programmed.
How urgent: Medium.
What we do: Program the module with factory software (we do this in-house).

P0603 – Internal Control Module Keep Alive Memory Error

What it means: ECU lost its memory.
Common causes: Battery disconnect, failing ECU, voltage.
How urgent: Low to medium.
What we do: Check power/ground; relearn procedures.

P0604 – Internal Control Module RAM Error

What it means: ECU RAM fault.
Common causes: ECU, voltage issues.
How urgent: Medium to high.
What we do: Power checks, then module.

P0605 – Internal Control Module ROM Error

What it means: ECU ROM fault.
Common causes: ECU, failed flash.
How urgent: Medium to high.
What we do: Reflash attempt, then module.

P0607 – Control Module Performance

What it means: ECU not performing.
Common causes: ECU, power/ground, software.
How urgent: Medium.
What we do: Software update first (many are fixed by a reflash).

P0610 – Control Module Vehicle Options Error

What it means: Module not coded for this vehicle’s options.
Common causes: Wrong or unprogrammed module.
How urgent: Medium.
What we do: Coding/programming with factory software.

P0613 – TCM Processor

What it means: Transmission module processor fault.
Common causes: TCM, power/ground.
How urgent: Medium to high.
What we do: Power checks, reflash, then module.

P0630 – VIN Not Programmed or Mismatch

What it means: The VIN in the module doesn’t match the car.
Common causes: Replaced module not programmed.
How urgent: Low (fails inspection).
What we do: VIN programming with factory software.

P1101 – MAF Sensor Out of Self-Test Range (GM/Hyundai/Kia)

What it means: MAF reading out of expected range.
Common causes: Intake leak, dirty MAF, PCV.
How urgent: Medium.
What we do: Intake leak and MAF check.

P1326 – Knock Sensor Detection System (Hyundai/Kia)

What it means: Engine vibration beyond limit detected (KSDS).
Common causes: Rod-bearing wear on affected Theta II engines; may be covered by recall/extended warranty.
How urgent: High.
What we do: We check the engine and point you to the manufacturer recall/warranty where it applies, before any paid repair.

P2004 – Intake Manifold Runner Control Stuck Open (Bank 1)

What it means: Intake runner flap stuck open.
Common causes: Runner control motor, flaps, linkage, carbon.
How urgent: Low to medium.
What we do: Actuator and flap test; common on Ford, Mazda, VW/Audi.

P2006 – Intake Manifold Runner Control Stuck Closed (Bank 1)

What it means: Runner flap stuck closed.
Common causes: Same as P2004.
How urgent: Low to medium.
What we do: Same as P2004.

P2015 – Intake Manifold Runner Position Sensor Range/Performance

What it means: Runner position sensor off.
Common causes: Sensor, flap linkage (common on VW/Audi 2.0T), carbon.
How urgent: Low to medium.
What we do: Sensor/flap test.

P0520 – Engine Oil Pressure Sensor/Switch Circuit

What it means: Oil pressure sensor circuit fault.
Common causes: Sensor, wiring.
How urgent: Medium (verify real pressure!).
What we do: Mechanical oil pressure test before anything else.

P0521 – Engine Oil Pressure Sensor Range/Performance

What it means: Oil pressure reading off.
Common causes: Sensor, actual low pressure, sludge.
How urgent: Medium to high.
What we do: Mechanical oil pressure test.

P0522 – Engine Oil Pressure Sensor Low

What it means: Oil pressure signal low.
Common causes: Sensor, wiring, low pressure.
How urgent: High if real.
What we do: Mechanical test, then sensor.

P0523 – Engine Oil Pressure Sensor High

What it means: Oil pressure signal high.
Common causes: Sensor, wiring.
How urgent: Medium.
What we do: Circuit test, sensor.

P0524 – Engine Oil Pressure Too Low

What it means: Actual low oil pressure.
Common causes: Low oil, worn pump, bearings, wrong oil.
How urgent: High (stop driving).
What we do: Mechanical pressure test; do not drive.

P06DD – Engine Oil Pressure Control Circuit Stuck Off

What it means: Two-stage oil pump solenoid fault.
Common causes: Oil pump solenoid, oil condition (GM/Chrysler).
How urgent: Medium.
What we do: Oil service, solenoid test.

P0541 – Intake Air Heater A Circuit Low

What it means: Intake heater circuit low (diesel).
Common causes: Heater, relay, wiring.
How urgent: Low.
What we do: Circuit test.

P0671 – Glow Plug Cylinder 1 Circuit (diesel)

What it means: Glow plug circuit fault.
Common causes: Glow plug, module, wiring.
How urgent: Low to medium.
What we do: Glow plug test.

P2002 – Diesel Particulate Filter Efficiency Below Threshold (Bank 1)

What it means: DPF not filtering as designed.
Common causes: Clogged DPF, failed regeneration, sensor.
How urgent: Medium.
What we do: Pressure sensor data and forced regeneration before replacement.

P2463 – Diesel Particulate Filter Soot Accumulation

What it means: DPF full of soot.
Common causes: Short trips preventing regen, failed regen, sensor.
How urgent: Medium.
What we do: Forced regeneration and driving advice.

U0073 – Control Module Communication Bus A Off

What it means: CAN bus is down.
Common causes: Shorted module, wiring, connector, low voltage.
How urgent: High.
What we do: Network isolation testing.

U0140 – Lost Communication With Body Control Module

What it means: Can’t talk to the BCM.
Common causes: Wiring, fuse, BCM power/ground.
How urgent: Medium to high.
What we do: Same approach as U0100.

U0164 – Lost Communication With HVAC Control Module

What it means: Can’t talk to the climate module.
Common causes: Wiring, fuse, module.
How urgent: Low to medium.
What we do: Same approach as U0100.

U0401 – Invalid Data Received From ECM/PCM

What it means: Engine computer sending bad data.
Common causes: ECU, software mismatch, wiring.
How urgent: Medium.
What we do: Software check and network test.

U0415 – Invalid Data Received From ABS Module

What it means: ABS sending bad data.
Common causes: ABS module, wheel speed sensors, wiring.
How urgent: Medium.
What we do: ABS module scan.

U1000 – Class 2 Communication Malfunction (GM)

What it means: GM network fault.
Common causes: Wiring, module, low voltage.
How urgent: Medium.
What we do: Network test.

U0001 – High Speed CAN Communication Bus

What it means: High-speed CAN fault.
Common causes: Wiring, module, connector.
How urgent: High.
What we do: Network isolation.

C0035 – Left Front Wheel Speed Sensor Circuit

What it means: ABS wheel speed sensor fault (C0040 RF, C0045 LR, C0050 RR).
Common causes: Sensor, tone ring, wiring, hub bearing.
How urgent: Medium (ABS/traction off).
What we do: Sensor live data; often a sensor or a rusted tone ring.

C0040 – Right Front Wheel Speed Sensor Circuit

What it means: RF wheel speed sensor fault.
Common causes: Sensor, tone ring, wiring.
How urgent: Medium.
What we do: Same as C0035.

C0045 – Left Rear Wheel Speed Sensor Circuit

What it means: LR wheel speed sensor fault.
Common causes: Sensor, tone ring, wiring.
How urgent: Medium.
What we do: Same as C0035.

C0050 – Right Rear Wheel Speed Sensor Circuit

What it means: RR wheel speed sensor fault.
Common causes: Sensor, tone ring, wiring.
How urgent: Medium.
What we do: Same as C0035.

C1201 – Engine Control System Malfunction (Toyota/Lexus ABS)

What it means: ABS disabled because of an engine code.
Common causes: Any engine fault.
How urgent: Medium.
What we do: Fix the engine code; the ABS code clears.

C0561 – System Disabled Information Stored (GM ABS)

What it means: ABS/traction disabled due to another fault.
Common causes: Engine/throttle/sensor fault elsewhere.
How urgent: Medium.
What we do: Find and fix the underlying code.

C0265 – EBCM Motor Relay Circuit (GM ABS)

What it means: ABS module relay fault.
Common causes: ABS module (common on older GM trucks).
How urgent: Medium.
What we do: Module test; repair services available.

B1318 – Battery Voltage Low (Ford)

What it means: Low voltage detected by a body module.
Common causes: Weak battery, alternator, terminals.
How urgent: Medium.
What we do: Battery/charging test.

B0001 – Driver Frontal Stage 1 Deployment Control

What it means: Airbag circuit fault.
Common causes: Clock spring, connector under seat, module.
How urgent: Medium (airbag light).
What we do: Airbag system scan; often a connector.

B1342 – ECU Is Defective (Ford)

What it means: Module reports itself defective.
Common causes: Module, power/ground.
How urgent: Medium to high.
What we do: Power checks before replacing.

Have one of these codes?

We diagnose with factory-level tools and fix only what’s broken. Any make or model. Bring a dealer estimate and we typically do the same repair for 30–50% less.

Book a Diagnostic Call 862-200-7040

Frequently asked questions

Can I keep driving with the check engine light on?

If the light is steady and the car drives normally, you can usually drive it to the shop. If the light is flashing, or the car is overheating, stalling or in limp mode, stop driving and call.

Does the code tell you exactly what part to replace?

No. The code points to a system. A P0420, for example, can be caused by an exhaust leak or a lazy oxygen sensor, not just the converter. RS Autowerks tests the system before replacing parts.

What does a diagnostic cost at RS Autowerks?

If your car failed NJ inspection, the checkup and estimate are free. Otherwise we quote the diagnostic up front and it is credited toward the repair if we do the work.

Will clearing the code fix the problem?

No. Clearing the code turns the light off until the fault happens again, and it resets the readiness monitors so the car fails NJ inspection as ‘not ready’.

Which makes can RS Autowerks diagnose?

All of them. BMW and MINI with ISTA, Audi/VW/Porsche with VCDS and ODIS, and Mercedes, Ford, GM, Chrysler/Jeep, Honda, Toyota, Nissan, Hyundai/Kia, Subaru and others with a professional Autel platform.

What is the cheapest check engine light fix?

A loose gas cap (P0455/P0457), a dirty mass airflow sensor, or a cracked vacuum hose. Those are always checked before anything expensive.

Can you fix transmission codes without a rebuild?

Often, yes. Many P07xx codes are a fluid service, a solenoid or a valve body. We tell you honestly when it is a rebuild, and whether that makes sense for the car’s value.

Written by Adam Jamhawi, owner of RS Autowerks in Wayne, NJ. Code definitions are generic OBD-II meanings; always confirm with a proper diagnosis before buying parts.

Check Engine, Transmission & ABS Codes Explained: 330+ Common OBD-II Codes and How We Fix Them