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.

P0631 — P0631 — VIN Not Programmed or Incompatible – TCM. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit, open or shorted wiring in the circuit.
P0632 — Odometer Not Programmed – ECM/PCM (P0632): 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, faulty sensor or actuator of the affected circuit.
P0633 — OBD2 code P0633 flags a problem with the sensor and actuator circuits (immobilizer key not programmed – ECM/PCM). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, open or shorted wiring in the circuit, poor ground connection.
P0634 — P0634 — PCM/ECM/TCM Internal Temperature Too High. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: corroded, loose or damaged connector, open or shorted wiring in the circuit, poor ground connection.
P0635 — OBD2 code P0635 flags a problem with the sensor and actuator circuits (power steering control circuit). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, poor ground connection, control module driver fault.
P0636 — OBD2 code P0636 flags a problem with the sensor and actuator circuits (power steering control circuit low). The car is usually drivable while you plan the repair. Common culprits: control module driver fault, blown fuse feeding the circuit, faulty sensor or actuator of the affected circuit.
P0637 — Power Steering Control Circuit High (P0637): 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 control module driver fault, blown fuse feeding the circuit, faulty sensor or actuator of the affected circuit.
P0638 — Throttle Actuator Control Range/Performance (Bank 1) (P0638): 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, wiring or connector faults in the throttle circuit.
P0639 — P0639 — Throttle Actuator Control Range/Performance (Bank 2). A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: failed electronic throttle motor, dirty throttle body or stuck throttle plate, intake air leaks after the MAF sensor.
P063A — Generator Voltage Sense Circuit (P063A): 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 faulty sensor or actuator of the affected circuit, control module driver fault, blown fuse feeding the circuit.
P063B — OBD2 code P063B flags a problem with the sensor and actuator circuits (generator voltage sense circuit range/performance). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit, control module driver fault.
P063C — P063C — Generator Voltage Sense Circuit Low. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: corroded, loose or damaged connector, poor ground connection, blown fuse feeding the circuit.
P063D — Generator Voltage Sense Circuit High (P063D): 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.
P063E — Auto Configuration Throttle Input Not Present (P063E): 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 failed electronic throttle motor, dirty throttle body or stuck throttle plate, intake air leaks after the MAF sensor.
P063F — Auto Configuration Engine Coolant Temperature Input Not Present (P063F): 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 low coolant level or air in the system, wiring faults in the sensor circuit, faulty coolant temperature sensor.
P0640 — Intake Air Heater Control Circuit (P0640): 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 intake air leaks after the MAF sensor, dirty throttle body or stuck throttle plate, faulty throttle position sensor or pedal sensor.
P0641 — Sensor Reference Voltage "A" Circuit Open (P0641): 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, corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit.
P0642 — Sensor Reference Voltage "A" Circuit Low (P0642): 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 control module driver fault, blown fuse feeding the circuit, poor ground connection.
P0643 — OBD2 code P0643 flags a problem with the sensor and actuator circuits (sensor reference voltage "A" circuit high). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, control module driver fault, corroded, loose or damaged connector.
P0644 — Driver Display Serial Communication Circuit (P0644): 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, control module driver fault, blown fuse feeding the circuit.
P0645 — P0645 — A/C Clutch Relay Control Circuit. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit, control module driver fault.
P0646 — A/C Clutch Relay Control Circuit Low (P0646): 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, corroded, loose or damaged connector.
P0647 — OBD2 code P0647 flags a problem with the sensor and actuator circuits (A/C clutch relay control circuit high). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.
P0648 — Immobilizer Lamp Control Circuit (P0648): 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.