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

• P0301 — P0301 — Cylinder 1 Misfire Detected. A fault in the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Typical causes: worn or fouled spark plugs, vacuum leak in the intake, low compression in the affected cylinder(s).
• P0302 — OBD2 code P0302 flags a problem with the engine misfire monitoring (cylinder 2 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: faulty crankshaft/camshaft position signal, worn or fouled spark plugs, failed ignition coil or coil wiring.
• P0303 — Cylinder 3 Misfire Detected (P0303): a powertrain (engine/transmission) fault affecting the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Most often caused by low compression in the affected cylinder(s), faulty crankshaft/camshaft position signal, clogged or leaking fuel injector.
• P0304 — OBD2 code P0304 flags a problem with the engine misfire monitoring (cylinder 4 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: failed ignition coil or coil wiring, clogged or leaking fuel injector, faulty crankshaft/camshaft position signal.
• P0305 — OBD2 code P0305 flags a problem with the engine misfire monitoring (cylinder 5 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: worn or fouled spark plugs, incorrect fuel pressure or a weak fuel pump, low compression in the affected cylinder(s).
• P0306 — Cylinder 6 Misfire Detected (P0306): a powertrain (engine/transmission) fault affecting the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Most often caused by faulty crankshaft/camshaft position signal, vacuum leak in the intake, clogged or leaking fuel injector.
• P0307 — OBD2 code P0307 flags a problem with the engine misfire monitoring (cylinder 7 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: clogged or leaking fuel injector, faulty crankshaft/camshaft position signal, failed ignition coil or coil wiring.
• P0308 — P0308 — Cylinder 8 Misfire Detected. A fault in the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Typical causes: incorrect fuel pressure or a weak fuel pump, vacuum leak in the intake, low compression in the affected cylinder(s).
• P0309 — P0309 — Cylinder 9 Misfire Detected. A fault in the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Typical causes: failed ignition coil or coil wiring, low compression in the affected cylinder(s), incorrect fuel pressure or a weak fuel pump.
• P0310 — P0310 — Cylinder 10 Misfire Detected. A fault in the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Typical causes: failed ignition coil or coil wiring, low compression in the affected cylinder(s), faulty crankshaft/camshaft position signal.
• P0311 — OBD2 code P0311 flags a problem with the engine misfire monitoring (cylinder 11 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: clogged or leaking fuel injector, failed ignition coil or coil wiring, low compression in the affected cylinder(s).
• P0312 — OBD2 code P0312 flags a problem with the engine misfire monitoring (cylinder 12 misfire detected). Short, gentle driving to a shop is usually possible. Common culprits: failed ignition coil or coil wiring, low compression in the affected cylinder(s), faulty crankshaft/camshaft position signal.
• P0313 — Misfire Detected with Low Fuel (P0313): a powertrain (engine/transmission) fault affecting the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Most often caused by incorrect fuel pressure or a weak fuel pump, worn or fouled spark plugs, clogged or leaking fuel injector.
• P0314 — Single Cylinder Misfire (Cylinder not Specified) (P0314): a powertrain (engine/transmission) fault affecting the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Most often caused by failed ignition coil or coil wiring, low compression in the affected cylinder(s), faulty crankshaft/camshaft position signal.
• P0315 — P0315 — Crankshaft Position System Variation Not Learned. A fault in the crankshaft position sensing. Driving is not recommended until fixed. Typical causes: failed crankshaft position sensor, ECM signal processing fault, incorrect sensor air gap.
• P0316 — P0316 — Misfire Detected On Startup (First 1000 Revolutions). A fault in the engine misfire monitoring. Short, gentle driving to a shop is usually possible. Typical causes: low compression in the affected cylinder(s), clogged or leaking fuel injector, failed ignition coil or coil wiring.
• P0317 — OBD2 code P0317 flags a problem with the sensor and actuator circuits (rough road hardware not present). 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.
• P0318 — Rough Road Sensor A Signal Circuit (P0318): 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, open or shorted wiring in the circuit, control module driver fault.
• P0319 — Rough Road Sensor B Signal Circuit (P0319): 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, poor ground connection, faulty sensor or actuator of the affected circuit.
• P0320 — Ignition/Distributor Engine Speed Input Circuit Malfunction (P0320): a powertrain (engine/transmission) fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by damaged coil wiring or connector, failed ignition coil or coil pack, faulty ignition control circuit in the ECM.
• P0321 — P0321 — Ignition/Distributor Engine Speed Input Circuit Range/Performance. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: faulty ignition control circuit in the ECM, damaged coil wiring or connector, worn spark plugs or wrong plug gap.
• P0322 — OBD2 code P0322 flags a problem with the ignition system (ignition/distributor engine speed input circuit no signal). Short, gentle driving to a shop is usually possible. Common culprits: moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM, worn spark plugs or wrong plug gap.
• P0323 — OBD2 code P0323 flags a problem with the ignition system (ignition/distributor engine speed input circuit intermittent). Short, gentle driving to a shop is usually possible. Common culprits: moisture or oil in the spark plug wells, faulty ignition control circuit in the ECM, worn spark plugs or wrong plug gap.
• P0324 — OBD2 code P0324 flags a problem with the knock (detonation) detection (knock control system error). Short, gentle driving to a shop is usually possible. Common culprits: damaged knock sensor wiring or connector, failed knock sensor, low-octane or contaminated fuel.