OBD2 fault codes explained
Plain-language explanations with real-world causes, ranked by how often they actually happen — not just the standard SAE definition. Have a code that is not listed? The AI diagnosis knows them all.
Air & fuel metering
P0016Crankshaft Position - Camshaft Position Correlation, Bank 1 Sensor AP0017Crankshaft Position - Camshaft Position Correlation, Bank 1 Sensor BP0100Mass or Volume Air Flow Circuit MalfunctionP0101Mass or Volume Air Flow Circuit Range/Performance ProblemP0102Mass or Volume Air Flow Circuit Low InputP0103Mass or Volume Air Flow Circuit High InputP0106Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance ProblemP0107Manifold Absolute Pressure/Barometric Pressure Circuit Low InputP0108Manifold Absolute Pressure/Barometric Pressure Circuit High InputP0110Intake Air Temperature Circuit MalfunctionP0111Intake Air Temperature Circuit Range/Performance ProblemP0112Intake Air Temperature Circuit Low InputP0113Intake Air Temperature Circuit High InputP0115Engine Coolant Temperature Circuit MalfunctionP0116Engine Coolant Temperature Circuit Range/Performance ProblemP0117Engine Coolant Temperature Circuit Low InputP0118Engine Coolant Temperature Circuit High InputP0120Throttle/Pedal Position Sensor/Switch "A" CircuitP0121Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance ProblemP0122Throttle/Pedal Position Sensor/Switch "A" Circuit Low InputP0123Throttle/Pedal Position Sensor/Switch "A" Circuit High InputP0125Insufficient Coolant Temperature for Closed Loop Fuel ControlP0128Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)P0130O2 Sensor Circuit (Bank 1 Sensor 1)P0131O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)P0132O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)P0133O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)P0134O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)P0135O2 Sensor Heater Circuit (Bank 1 Sensor 1)P0136O2 Sensor Circuit (Bank 1 Sensor 2)P0141O2 Sensor Heater Circuit (Bank 1 Sensor 2)P0171System Too Lean (Bank 1)P0172System Too Rich (Bank 1)P0174System Too Lean (Bank 2)P0175System Too Rich (Bank 2)P0201Injector Circuit/Open - Cylinder 1P0202Injector Circuit/Open - Cylinder 2P0203Injector Circuit/Open - Cylinder 3P0204Injector Circuit/Open - Cylinder 4P0217Engine Coolant Over Temperature ConditionP0230Fuel Pump Primary CircuitP0261Cylinder 1 Injector Circuit Low
Ignition & misfires
P0300Random/Multiple Cylinder Misfire DetectedP0301Cylinder 1 Misfire DetectedP0302Cylinder 2 Misfire DetectedP0303Cylinder 3 Misfire DetectedP0304Cylinder 4 Misfire DetectedP0305Cylinder 5 Misfire DetectedP0306Cylinder 6 Misfire DetectedP0325Knock Sensor 1 Circuit (Bank 1 or Single Sensor)P0327Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor)P0335Crankshaft Position Sensor A CircuitP0336Crankshaft Position Sensor A Circuit Range/PerformanceP0340Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor)P0341Camshaft Position Sensor A Circuit Range/Performance (Bank 1 or Single Sensor)P0365Camshaft Position Sensor B Circuit (Bank 1)P0369Camshaft Position Sensor B Circuit Intermittent (Bank 1)P0380Glow Plug/Heater Circuit A
Emissions systems
P0401Exhaust Gas Recirculation Flow Insufficient DetectedP0402Exhaust Gas Recirculation Flow Excessive DetectedP0403Exhaust Gas Recirculation Control CircuitP0404Exhaust Gas Recirculation Control Circuit Range/PerformanceP0410Secondary Air Injection System MalfunctionP0420Catalyst System Efficiency Below Threshold (Bank 1)P0430Catalyst System Efficiency Below Threshold (Bank 2)P0440Evaporative Emission Control System MalfunctionP0442Evaporative Emission Control System Leak Detected (Small Leak)P0446Evaporative Emission Control System Vent Control Circuit MalfunctionP0455Evaporative Emission Control System Leak Detected (Gross Leak)P0456Evaporative Emission Control System Leak Detected (Very Small Leak)P0457Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)P0460Fuel Level Sensor CircuitP0461Fuel Level Sensor Circuit Range/PerformanceP0462Fuel Level Sensor Circuit Low InputP0463Fuel Level Sensor Circuit High Input
Speed, idle & voltage
P0500Vehicle Speed Sensor AP0501Vehicle Speed Sensor A Range/PerformanceP0505Idle Air Control SystemP0506Idle Air Control System RPM Lower Than ExpectedP0507Idle Air Control System RPM Higher Than ExpectedP0560System VoltageP0562System Voltage LowP0563System Voltage High
Control units
P0601Internal Control Module Memory Check Sum ErrorP0602Control Module Programming ErrorP0603Internal Control Module Keep Alive Memory ErrorP0604Internal Control Module Random Access Memory (RAM) ErrorP0605Internal Control Module Read Only Memory (ROM) ErrorP0606Control Module Processor Fault
Transmission
P0700Transmission Control System Malfunction (MIL Request)P0715Input/Turbine Speed Sensor A Circuit MalfunctionP0720Output Speed Sensor Circuit MalfunctionP0730Incorrect Gear RatioP0740Torque Converter Clutch Circuit MalfunctionP0741Torque Converter Clutch Circuit Performance or Stuck OffP0750Shift Solenoid A Malfunction