OBD2 Fault Code Library

Free lookup for thousands of OBD2 trouble codes: filter by family, read short meanings, and open deeper articles. Desktop ELM327 scanner with live data and AI guidance.

OBD2 symptoms

Look up diagnostic trouble codes by what the car is doing: misfire, overheating, rough idle, a check engine light, and other common symptoms.

P0503 — OBD2 code P0503 flags a problem with the sensor and actuator circuits (vehicle speed sensor "A" intermittent/erratic/high). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, corroded, loose or damaged connector, control module driver fault.
P0504 — OBD2 code P0504 flags a problem with the ABS / stability control (brake switch "A"/"B" correlation). Short, gentle driving to a shop is usually possible. Common culprits: damaged sensor wiring or corroded connector, blown fuse or low voltage to the ABS module, faulty ABS module or pump motor.
P0505 — OBD2 code P0505 flags a problem with the sensor and actuator circuits (idle control system malfunction). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, corroded, loose or damaged connector, poor ground connection.
P0506 — Idle Control System RPM Lower Than Expected (P0506): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by blown fuse feeding the circuit, faulty sensor or actuator of the affected circuit, poor ground connection.
P0507 — OBD2 code P0507 flags a problem with the sensor and actuator circuits (idle control system RPM higher than expected). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, poor ground connection, faulty sensor or actuator of the affected circuit.
P0508 — Idle Air Control System Circuit Low (P0508): a powertrain (engine/transmission) fault affecting the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Most often caused by contaminated or failed MAF/MAP sensor, failed electronic throttle motor, dirty throttle body or stuck throttle plate.
P0509 — P0509 — Idle Air Control System Circuit High. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: faulty throttle position sensor or pedal sensor, contaminated or failed MAF/MAP sensor, dirty throttle body or stuck throttle plate.
P050A — P050A — Cold Start Idle Air Control System Performance. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: wiring or connector faults in the throttle circuit, dirty throttle body or stuck throttle plate, intake air leaks after the MAF sensor.
P050B — Cold Start Ignition Timing Performance (P050B): a powertrain (engine/transmission) fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by moisture or oil in the spark plug wells, worn spark plugs or wrong plug gap, damaged coil wiring or connector.
P050C — Cold Start Engine Coolant Temperature Performance (P050C): a powertrain (engine/transmission) fault affecting the engine cooling and temperature control. Short, gentle driving to a shop is usually possible. Most often caused by failed cooling fan or fan relay, thermostat stuck open or closed, faulty coolant temperature sensor.
P050D — OBD2 code P050D flags a problem with the sensor and actuator circuits (cold start rough idle). The car is usually drivable while you plan the repair. Common culprits: poor ground connection, corroded, loose or damaged connector, open or shorted wiring in the circuit.
P050E — OBD2 code P050E flags a problem with the sensor and actuator circuits (cold start engine exhaust temperature too low). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, open or shorted wiring in the circuit, control module driver fault.
P050F — Brake Assist Vacuum Too Low (P050F): a powertrain (engine/transmission) fault affecting the ABS / stability control. Short, gentle driving to a shop is usually possible. Most often caused by damaged sensor wiring or corroded connector, faulty ABS module or pump motor, damaged tone (reluctor) ring on the hub.
P0510 — OBD2 code P0510 flags a problem with the throttle and intake air metering (closed throttle position switch malfunction). Short, gentle driving to a shop is usually possible. Common culprits: faulty throttle position sensor or pedal sensor, wiring or connector faults in the throttle circuit, intake air leaks after the MAF sensor.
P0511 — P0511 — Idle Air Control Circuit. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: wiring or connector faults in the throttle circuit, intake air leaks after the MAF sensor, faulty throttle position sensor or pedal sensor.
P0512 — P0512 — Starter Request Circuit. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, open or shorted wiring in the circuit, poor ground connection.
P0513 — Incorrect Immobilizer Key (P0513): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit, open or shorted wiring in the circuit.
P0514 — Battery Temperature Sensor Circuit Range/Performance (P0514): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by open or shorted wiring in the circuit, blown fuse feeding the circuit, poor ground connection.
P0515 — OBD2 code P0515 flags a problem with the sensor and actuator circuits (battery temperature sensor circuit). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector, blown fuse feeding the circuit.
P0516 — Battery Temperature Sensor Circuit Low (P0516): a powertrain (engine/transmission) fault affecting the sensor and actuator circuits. The car is usually drivable while you plan the repair. Most often caused by poor ground connection, open or shorted wiring in the circuit, blown fuse feeding the circuit.
P0517 — P0517 — Battery Temperature Sensor Circuit High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, poor ground connection, open or shorted wiring in the circuit.
P0518 — P0518 — Idle Air Control Circuit Intermittent. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: dirty throttle body or stuck throttle plate, contaminated or failed MAF/MAP sensor, intake air leaks after the MAF sensor.
P0519 — Idle Air Control System Performance (P0519): a powertrain (engine/transmission) fault affecting the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Most often caused by dirty throttle body or stuck throttle plate, wiring or connector faults in the throttle circuit, intake air leaks after the MAF sensor.
P051A — OBD2 code P051A flags a problem with the sensor and actuator circuits (crankcase pressure sensor circuit). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit.