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.

P0123 — P0123 — Throttle Position Sensor/Switch A Circuit High Input. 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, failed electronic throttle motor.
P0124 — P0124 — Throttle Position Sensor/Switch A Circuit Intermittent. A fault in the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Typical causes: contaminated or failed MAF/MAP sensor, faulty throttle position sensor or pedal sensor, intake air leaks after the MAF sensor.
P0125 — Insufficient Coolant Temperature for Closed Loop Fuel Control (P0125): 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, faulty coolant temperature sensor, wiring faults in the sensor circuit.
P0126 — OBD2 code P0126 flags a problem with the engine cooling and temperature control (insufficient coolant temperature for stable operation). Short, gentle driving to a shop is usually possible. Common culprits: wiring faults in the sensor circuit, faulty coolant temperature sensor, thermostat stuck open or closed.
P0127 — P0127 — Intake Air Temperature Too High. 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, faulty throttle position sensor or pedal sensor, wiring or connector faults in the throttle circuit.
P0128 — Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) (P0128): 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 water pump or radiator issues, failed cooling fan or fan relay, faulty coolant temperature sensor.
P0129 — P0129 — Barometric Pressure Too Low. 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, control module driver fault, faulty sensor or actuator of the affected circuit.
P012A — P012A — Turbocharger/Supercharger Inlet Pressure Sensor Circuit (Downstream of throttle valve). A fault in the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Typical causes: stuck wastegate or faulty boost control solenoid, faulty boost pressure sensor, vacuum or actuator line damage.
P012B — P012B — Turbocharger/Supercharger Inlet Pressure Sensor Circuit Range/Performance (Downstream of throttle valve). A fault in the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Typical causes: faulty boost pressure sensor, worn turbocharger, stuck wastegate or faulty boost control solenoid.
P012C — Turbocharger/Supercharger Inlet Pressure Sensor Circuit Low (Downstream of throttle valve) (P012C): a powertrain (engine/transmission) fault affecting the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Most often caused by faulty boost pressure sensor, clogged intake or exhaust (DPF/cat), vacuum or actuator line damage.
P012D — OBD2 code P012D flags a problem with the turbocharger / supercharger boost control (turbocharger/supercharger inlet pressure sensor circuit high (downstream of throttle valve)). Short, gentle driving to a shop is usually possible. Common culprits: boost leak in intercooler piping or hoses, stuck wastegate or faulty boost control solenoid, vacuum or actuator line damage.
P012E — P012E — Turbocharger/Supercharger Inlet Pressure Sensor Circuit Intermittent/Erratic (Downstream of throttle valve). A fault in the turbocharger / supercharger boost control. Short, gentle driving to a shop is usually possible. Typical causes: clogged intake or exhaust (DPF/cat), faulty boost pressure sensor, stuck wastegate or faulty boost control solenoid.
P0130 — P0130 — 02 Sensor Circuit Malfunction (Bank I Sensor 1). A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: blown fuse feeding the circuit, poor ground connection, faulty sensor or actuator of the affected circuit.
P0131 — P0131 — 02 Sensor Circuit Low Voltage (Bank I Sensor I). 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, poor ground connection, corroded, loose or damaged connector.
P0132 — 02 Sensor Circuit High Voltage (Bank I Sensor 1) (P0132): 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, poor ground connection, blown fuse feeding the circuit.
P0133 — OBD2 code P0133 flags a problem with the sensor and actuator circuits (02 sensor circuit slow response (bank 1 sensor 1)). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, open or shorted wiring in the circuit, corroded, loose or damaged connector.
P0134 — 02 Sensor Circuit No Activity Detected (Bank I Sensor 1) (P0134): 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, poor ground connection.
P0135 — OBD2 code P0135 flags a problem with the sensor and actuator circuits (02 sensor heater circuit malfunction (bank 1 sensor 1)). The car is usually drivable while you plan the repair. Common culprits: control module driver fault, open or shorted wiring in the circuit, corroded, loose or damaged connector.
P0136 — OBD2 code P0136 flags a problem with the sensor and actuator circuits (02 sensor circuit malfunction (bank i sensor 2)). 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, open or shorted wiring in the circuit.
P0137 — OBD2 code P0137 flags a problem with the sensor and actuator circuits (02 sensor circuit low voltage (bank i sensor 2)). The car is usually drivable while you plan the repair. Common culprits: corroded, loose or damaged connector, blown fuse feeding the circuit, open or shorted wiring in the circuit.
P0138 — 02 Sensor Circuit High Voltage (Bank I Sensor 2) (P0138): 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, faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit.
P0139 — OBD2 code P0139 flags a problem with the sensor and actuator circuits (02 sensor circuit slow response (bank 1 sensor 2)). The car is usually drivable while you plan the repair. Common culprits: faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit, poor ground connection.
P013A — OBD2 code P013A flags a problem with the oxygen sensor circuit (O2 sensor slow response - rich to lean (bank 1 sensor 2)). The car is usually drivable while you plan the repair. Common culprits: ECM signal circuit fault, aged or contaminated oxygen sensor, blown sensor heater fuse.
P013B — P013B — O2 Sensor Slow Response - Lean to Rich (Bank 1 Sensor 2). A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: aged or contaminated oxygen sensor, exhaust leak near the sensor, ECM signal circuit fault.