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.

• Engine misfire
• Engine overheating
• Rough idle
• Check engine light
• Poor fuel economy
• Hard starting
• Engine stalling
• Catalytic converter efficiency
• Oxygen sensor fault
• EVAP leak
• Thermostat not reaching temperature
• Lean air-fuel mixture
• Rich air-fuel mixture
• EGR flow fault
• Engine knock
• Charging system
• Throttle position
• Mass airflow sensor
• Turbo underboost
• Coolant temperature sensor
• Transmission fault

• P0840 — P0840 — Transmission Fluid Pressure Sensor/Switch "A" Circuit. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: faulty transmission speed sensor, internal mechanical wear (clutches, torque converter), wiring or connector faults in the valve body harness.
• P0841 — OBD2 code P0841 flags a problem with the automatic transmission control (transmission fluid pressure sensor/switch "A" circuit range/performance). Short, gentle driving to a shop is usually possible. Common culprits: faulty transmission speed sensor, valve body wear, failed shift or pressure control solenoid.
• P0842 — Transmission Fluid Pressure Sensor/Switch "A" Circuit Low (P0842): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by internal mechanical wear (clutches, torque converter), faulty transmission speed sensor, low or degraded transmission fluid.
• P0843 — Transmission Fluid Pressure Sensor/Switch "A" Circuit High (P0843): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by internal mechanical wear (clutches, torque converter), faulty transmission speed sensor, valve body wear.
• P0844 — P0844 — Transmission Fluid Pressure Sensor/Switch "A" Circuit Intermittent. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: internal mechanical wear (clutches, torque converter), faulty transmission speed sensor, failed shift or pressure control solenoid.
• P0845 — Transmission Fluid Pressure Sensor/Switch "B" Circuit (P0845): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by failed shift or pressure control solenoid, valve body wear, wiring or connector faults in the valve body harness.
• P0846 — P0846 — Transmission Fluid Pressure Sensor/Switch "B" Circuit Range/Performance. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: wiring or connector faults in the valve body harness, low or degraded transmission fluid, valve body wear.
• P0847 — P0847 — Transmission Fluid Pressure Sensor/Switch "B" Circuit Low. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: low or degraded transmission fluid, failed shift or pressure control solenoid, valve body wear.
• P0848 — P0848 — Transmission Fluid Pressure Sensor/Switch "B" Circuit High. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: failed shift or pressure control solenoid, internal mechanical wear (clutches, torque converter), valve body wear.
• P0849 — Transmission Fluid Pressure Sensor/Switch "B" Circuit Intermittent (P0849): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by low or degraded transmission fluid, failed shift or pressure control solenoid, valve body wear.
• P084A — OBD2 code P084A flags a problem with the automatic transmission control (transmission fluid pressure sensor/switch "H" circuit). Short, gentle driving to a shop is usually possible. Common culprits: failed shift or pressure control solenoid, wiring or connector faults in the valve body harness, faulty transmission speed sensor.
• P084B — Transmission Fluid Pressure Sensor/Switch "H" Circuit Range/Performance (P084B): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by valve body wear, internal mechanical wear (clutches, torque converter), low or degraded transmission fluid.
• P084C — Transmission Fluid Pressure Sensor/Switch "H" Circuit Low (P084C): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by internal mechanical wear (clutches, torque converter), low or degraded transmission fluid, valve body wear.
• P084D — Transmission Fluid Pressure Sensor/Switch "H" Circuit High (P084D): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by valve body wear, wiring or connector faults in the valve body harness, failed shift or pressure control solenoid.
• P084E — Transmission Fluid Pressure Sensor/Switch "H" Circuit Intermittent (P084E): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by low or degraded transmission fluid, internal mechanical wear (clutches, torque converter), faulty transmission speed sensor.
• P084F — Park/Neutral Switch Output Circuit (P084F): 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, control module driver fault, poor ground connection.
• P0850 — P0850 — Park/Neutral Switch Input Circuit. 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, corroded, loose or damaged connector, blown fuse feeding the circuit.
• P0851 — P0851 — Park/Neutral Switch Input Circuit Low. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, blown fuse feeding the circuit, poor ground connection.
• P0852 — Park/Neutral Switch Input Circuit High (P0852): 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, poor ground connection, control module driver fault.
• P0853 — Drive Switch Input Circuit (P0853): 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.
• P0854 — Drive Switch Input Circuit Low (P0854): 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, open or shorted wiring in the circuit.
• P0855 — P0855 — Drive Switch Input Circuit High. 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, poor ground connection.
• P0856 — P0856 — Traction Control Input Signal. A fault in the ABS / stability control. Short, gentle driving to a shop is usually possible. Typical causes: blown fuse or low voltage to the ABS module, faulty ABS module or pump motor, damaged sensor wiring or corroded connector.
• P0857 — P0857 — Traction Control Input Signal Range/Performance. A fault in the ABS / stability control. Short, gentle driving to a shop is usually possible. Typical causes: damaged sensor wiring or corroded connector, faulty ABS module or pump motor, failed wheel speed sensor.