OBD-II diagnostic trouble code lookup
Curated catalog of the most-Googled OBD-II codes — definitions grounded in SAE J2012 / ISO 15031-6, common causes from real shop experience, and a direct link to ask the corpus for vehicle-specific diagnosis.
Engine, transmission, and emissions-related codes — the largest DTC family by volume. Most fault codes you'll see start with P.
Lighting, locks, immobilizer, climate, airbag SRS, infotainment, and other body-system codes.
ABS, stability control, steering, suspension, and tire pressure monitoring codes.
CAN bus communication and inter-module networking faults. Almost always a downstream report of a deeper problem.
Powertrain codes
Engine, transmission, and emissions-related codes — the largest DTC family by volume. Most fault codes you'll see start with P.
The ECM has detected an issue with the MAF sensor circuit. Voltage is either out of range or the signal is missing entirely.
Fuel trims indicate the engine is running lean on Bank 1 — too much air relative to fuel. Common on aging vehicles with vacuum leaks.
The ECM has detected misfires across more than one cylinder. Multi-cylinder misfires typically point at fuel, spark, or compression issues affecting the whole engine, not a single coil/injector.
The downstream O2 sensor on Bank 1 is mirroring the upstream sensor too closely, indicating the catalytic converter is no longer effectively storing oxygen.
The Engine Control Module has detected an internal processor fault — its own self-test has failed. Almost always indicates the ECM is failing or already failed.
The Transmission Control Module (TCM) has reported a fault to the ECM. P0700 itself is generic — always pull the secondary TCM-specific codes (P07xx) for the actual problem.
The torque converter lockup clutch is not engaging or disengaging as commanded. Often felt as judder around 40-50 mph during light cruising.
The EGR cooler bypass actuator is not responding to ECM commands. Common on EU diesels with EDC17 controllers.
Body codes
Lighting, locks, immobilizer, climate, airbag SRS, infotainment, and other body-system codes.
The vehicle's immobilizer system did not receive a valid key authentication. Engine will crank but not start. Common Toyota / Lexus code.
The immobilizer antenna ring around the ignition lock cylinder is not transmitting the RF challenge to the key transponder. Vehicle will not start.
The Body Control Module has detected an internal fault. May affect lighting, locks, wipers, or other body functions depending on the vehicle.
Chassis codes
ABS, stability control, steering, suspension, and tire pressure monitoring codes.
The ABS / VSC module sees an active engine control fault and disables traction-related interventions until the engine code is cleared.
The ABS or stability-control module sees a configuration that doesn't match the vehicle's expected setup — often after a module swap.
Network codes
CAN bus communication and inter-module networking faults. Almost always a downstream report of a deeper problem.
Another module on the CAN bus has lost communication with the Engine Control Module. The ECM may be unpowered, off the bus, or fully failed.
The high-speed CAN bus has gone silent or is showing electrical fault. All modules on that bus segment are affected.
A module reports it can no longer see the BCM on the network. Often appears together with B-codes from the BCM itself.
The reporting module cannot see the ABS module on the CAN bus. ABS warning light is typically also illuminated.
Don't see your code?
We catalog the most-Googled codes by hand to keep the entries accurate. For anything not on the list, ask the forums directly — the corpus has 14,000+ indexed threads covering vehicle-specific symptoms, fix patterns, and known TSBs.
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