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

• P2856 — OBD2 code P2856 flags a problem with the sensor and actuator circuits (clutch "B" pressure charge performance). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, control module driver fault, corroded, loose or damaged connector.
• P2857 — Clutch "A" Pressure Engagement Performance (P2857): 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, faulty sensor or actuator of the affected circuit.
• P2858 — P2858 — Clutch "B" Pressure Engagement Performance. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: poor ground connection, control module driver fault, corroded, loose or damaged connector.
• P285A — OBD2 code P285A flags a problem with the sensor and actuator circuits (clutch "B" pressure disengagement performance). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, blown fuse feeding the circuit, poor ground connection.
• P2A00 — P2A00 — O2 Sensor Circuit Range/Performance Bank 1 Sensor 1. A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: ECM signal circuit fault, aged or contaminated oxygen sensor, oil or coolant contamination of the sensor tip.
• P2A02 — O2 Sensor Circuit Range/Performance Bank 1 Sensor 3 (P2A02): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by ECM signal circuit fault, blown sensor heater fuse, damaged sensor wiring or connector.
• P2A03 — OBD2 code P2A03 flags a problem with the oxygen sensor circuit (O2 sensor circuit range/performance bank 2 sensor 1). The car is usually drivable while you plan the repair. Common culprits: damaged sensor wiring or connector, exhaust leak near the sensor, blown sensor heater fuse.
• P2A04 — O2 Sensor Circuit Range/Performance Bank 2 Sensor 2 (P2A04): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by oil or coolant contamination of the sensor tip, damaged sensor wiring or connector, aged or contaminated oxygen sensor.
• P2A05 — OBD2 code P2A05 flags a problem with the oxygen sensor circuit (O2 sensor circuit range/performance bank 2 sensor 3). The car is usually drivable while you plan the repair. Common culprits: exhaust leak near the sensor, damaged sensor wiring or connector, ECM signal circuit fault.
• P2A06 — P2A06 — O2 Sensor Negative Voltage Bank 1 Sensor 1. A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: aged or contaminated oxygen sensor, ECM signal circuit fault, damaged sensor wiring or connector.
• P2A07 — O2 Sensor Negative Voltage Bank 1 Sensor 2 (P2A07): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by ECM signal circuit fault, blown sensor heater fuse, exhaust leak near the sensor.
• P2A08 — OBD2 code P2A08 flags a problem with the oxygen sensor circuit (O2 sensor negative voltage bank 1 sensor 3). The car is usually drivable while you plan the repair. Common culprits: ECM signal circuit fault, exhaust leak near the sensor, blown sensor heater fuse.
• P2A09 — O2 Sensor Negative Voltage Bank 2 Sensor 1 (P2A09): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by ECM signal circuit fault, aged or contaminated oxygen sensor, exhaust leak near the sensor.
• P2A10 — O2 Sensor Negative Voltage Bank 2 Sensor 2 (P2A10): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by blown sensor heater fuse, oil or coolant contamination of the sensor tip, aged or contaminated oxygen sensor.
• P2BA9 — NOx Exceedence - Insufficient Reagent Quality (P2BA9): 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, open or shorted wiring in the circuit, control module driver fault.
• P2BAA — P2BAA — NOx Exceedence - Low Reagent Consumption. 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, blown fuse feeding the circuit.
• P2BAB — OBD2 code P2BAB flags a problem with the exhaust gas recirculation (EGR) system (nox exceedence - incorrect EGR flow). The car is usually drivable while you plan the repair. Common culprits: faulty EGR solenoid or wiring, vacuum leaks in EGR control lines, carbon buildup blocking the EGR valve or passages.
• P2BAD — OBD2 code P2BAD flags a problem with the sensor and actuator circuits (nox exceedence - root cause unknown). 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, open or shorted wiring in the circuit.
• P3400 — OBD2 code P3400 flags a problem with the sensor and actuator circuits (cylinder deactivation system bank 1). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, poor ground connection, corroded, loose or damaged connector.
• P3401 — OBD2 code P3401 flags a problem with the sensor and actuator circuits (cylinder 1 deactivation/intake valve control circuit/open). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, poor ground connection, faulty sensor or actuator of the affected circuit.
• P3402 — Cylinder 1 Deactivation/Intake Valve Control Circuit Performance (P3402): 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, open or shorted wiring in the circuit, corroded, loose or damaged connector.
• P3404 — Cylinder 1 Deactivation/Intake Valve Control Circuit High (P3404): 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, open or shorted wiring in the circuit, blown fuse feeding the circuit.
• P3405 — P3405 — Cylinder 1 Exhaust Valve Control Circuit/Open. 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, control module driver fault, open or shorted wiring in the circuit.
• P3406 — P3406 — Cylinder 1 Exhaust Valve Control Circuit Performance. 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, faulty sensor or actuator of the affected circuit.