OBD-II Code Library

Every code explained in plain English, with the specific scan-tool values a technician should actually see. No "could be this" — guided, step-by-step diagnostics from real techs.

• P0011Camshaft Position - Timing Over-Advanced (Bank 1 Intake)Intake cam is more advanced than the PCM commanded — VVT solenoid, oil viscosity, or phaser issue.
• P0016Crankshaft / Camshaft Position Correlation (Bank 1 Sensor A)PCM sees the cam and crank are out of sync — timing chain stretched, jumped a tooth, or VVT phaser stuck.
• P003ATurbocharger Boost Control Position Not LearnedVGT actuator position feedback isn't matching commanded — vanes likely stuck or actuator failed.
• P0087Fuel Rail/System Pressure Too LowPCM commanded fuel pressure and the rail sensor isn't seeing it — the system can't keep up.
• P0088Fuel Rail / System Pressure Too HighActual fuel rail pressure is exceeding the commanded pressure — regulator or sensor problem.
• P0101MAF Sensor Range/PerformanceMass airflow sensor reading doesn't match what the PCM expects for current engine load.
• P0102Mass Air Flow Sensor Circuit Low InputMAF signal is reading lower than physically possible for the engine's current operating state.
• P0103Mass Air Flow Sensor Circuit High InputMAF signal is reading higher than physically possible — usually a wiring short or failed sensor.
• P0113Intake Air Temperature Sensor Circuit High InputIAT signal voltage too high — sensor reading impossibly cold. Open wire or failed sensor.
• P0117Engine Coolant Temperature Sensor Circuit Low InputECT signal reading lower voltage than possible — usually shorted-to-ground wire or failed sensor.
• P0122Throttle / Pedal Position Sensor 'A' Circuit Low InputTPS signal voltage dropped below the minimum allowed — usually an open signal wire or failed sensor.
• P0128Coolant Temperature Below Thermostat Regulating TemperatureEngine isn't reaching operating temp in the time the PCM expects — thermostat stuck open.
• P0135O2 Sensor Heater Circuit Malfunction (B1S1)The heater inside the upstream oxygen sensor isn't drawing the right current.
• P0171System Too Lean (Bank 1)Long-term fuel trim is pushing positive — PCM is adding fuel to compensate for a lean condition.
• P0174System Too Lean (Bank 2)Same as P0171 but on bank 2.
• P0201Injector Circuit / Open — Cylinder 1PCM isn't seeing the injector on cylinder 1 respond electrically when it commands it.
• P0234Turbocharger Overboost ConditionBoost pressure exceeded the maximum allowed — wastegate or boost control problem.
• P0299Turbocharger Underboost ConditionPCM commanded boost and the MAP/boost sensor didn't see what it asked for.
• P0300Random / Multiple Cylinder Misfire DetectedPCM is seeing misfires across multiple cylinders, not isolated to one.
• P0301Cylinder 1 Misfire DetectedPCM has isolated misfires to cylinder 1 specifically.
• P0325Knock Sensor 1 Circuit Malfunction (Bank 1)PCM isn't getting a proper signal from the knock sensor — usually a failed sensor or wiring fault.
• P0335Crankshaft Position Sensor 'A' Circuit MalfunctionPCM isn't getting a valid crank signal — the king of no-start codes.
• P0340Camshaft Position Sensor 'A' Circuit MalfunctionPCM is missing or seeing a bad signal from the camshaft position sensor.
• P0401Exhaust Gas Recirculation Flow Insufficient DetectedEGR was commanded to flow and the PCM didn't see the expected effect — passages or valve are restricted.
• P0411Secondary Air Injection System Incorrect Flow DetectedThe cold-start air pump system isn't pushing the airflow the PCM expected.
• P0420Catalyst System Efficiency Below Threshold (Bank 1)PCM sees the catalytic converter isn't cleaning the exhaust like it should on bank 1.
• P0430Catalyst System Efficiency Below Threshold (Bank 2)Same as P0420 but on bank 2 (the other side of a V-engine).
• P0442EVAP System Small Leak DetectedFuel vapor system has a small leak — usually under 0.040 inches. Often the gas cap.
• P0455EVAP System Gross Leak DetectedLarge leak in the evaporative emissions system — usually the gas cap or a major hose.
• P0496EVAP System High Purge FlowPurge valve is flowing fuel vapor when it shouldn't be — usually a purge solenoid stuck open.
• P0500Vehicle Speed Sensor 'A' MalfunctionPCM isn't seeing a vehicle speed signal — affects shifting, torque converter lockup, cruise, and speedometer.
• P0507Idle Air Control System RPM Higher Than ExpectedIdle is sitting above the target and the PCM has already closed the throttle as far as it can.
• P0521Engine Oil Pressure Sensor / Switch Range / PerformanceOil pressure reading doesn't match what the PCM expects for current RPM. Verify with a mechanical gauge before driving.
• P0606PCM Processor FaultThe PCM ran an internal self-test and failed it. The computer is reporting itself as faulty.
• P0671Cylinder 1 Glow Plug Circuit MalfunctionGlow plug control module isn't seeing the right current draw on cylinder 1's glow plug circuit.
• P0700Transmission Control System Malfunction (Request from TCM)Not a fault itself — it's the TCM telling the PCM 'I have a transmission code, go look at me.'
• P0741Torque Converter Clutch Circuit Performance / Stuck OffTCC isn't locking up when the TCM commands it — slipping converter or solenoid problem.
• P2002Diesel Particulate Filter Efficiency Below Threshold (Bank 1)DPF isn't trapping soot like it should — or the differential pressure readings say it's not working.
• P204FReductant System Performance (DEF / SCR)DEF system can't maintain proper dosing or pressure — pump, line, or injector problem.
• P2096Post Catalyst Fuel Trim System Too Lean (Bank 1)Downstream O2 sensor on bank 1 is consistently reading lean — fuel trim correction hit its lean limit.
• P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)DEF / SCR system isn't reducing NOx like it should. Bad DEF, dosing problem, or failed NOx sensor.
• P2463Diesel Particulate Filter Restriction — Soot AccumulationDPF differential pressure is too high — filter loaded with soot and can't regen its way out.
• P2563Turbocharger Boost Control Position Sensor Circuit Range/PerformanceVGT actuator position sensor isn't reading where the PCM expects — usually a VGT actuator going bad.
• SPN 3361DEF Dosing Valve / Reductant Injector FaultJ1939 fault on the DEF injector that sprays into the SCR — circuit, flow, or actuator problem.
• SPN 5246Aftertreatment SCR Operator Inducement — SevereEngine has entered the inducement / derate path because an aftertreatment fault wasn't resolved in time.
• U0100Lost Communication with ECM/PCM 'A'Another module on the network can't talk to the engine PCM. CAN bus or PCM power problem.

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