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.

P2344 — OBD2 code P2344 flags a problem with the knock (detonation) detection (cylinder 9 above knock threshold). Short, gentle driving to a shop is usually possible. Common culprits: engine carbon buildup causing real detonation, failed knock sensor, low-octane or contaminated fuel.
P2346 — P2346 — Cylinder 11 Above Knock Threshold. A fault in the knock (detonation) detection. Short, gentle driving to a shop is usually possible. Typical causes: loose sensor mounting or incorrect torque, failed knock sensor, damaged knock sensor wiring or connector.
P2347 — Cylinder 12 Above Knock Threshold (P2347): a powertrain (engine/transmission) fault affecting the knock (detonation) detection. Short, gentle driving to a shop is usually possible. Most often caused by engine carbon buildup causing real detonation, damaged knock sensor wiring or connector, failed knock sensor.
P2403 — P2403 — Evaporative Emission System Leak Detection Pump Sense Circuit/Open. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: saturated or damaged charcoal canister, cracked EVAP hoses or lines, loose, damaged or wrong fuel cap.
P2404 — OBD2 code P2404 flags a problem with the evaporative emission (EVAP) system (evaporative emission system leak detection pump sense circuit range/performance). The car is usually drivable while you plan the repair. Common culprits: faulty purge valve (canister purge solenoid), cracked EVAP hoses or lines, small leak in the fuel tank or filler neck.
P2405 — Evaporative Emission System Leak Detection Pump Sense Circuit Low (P2405): a powertrain (engine/transmission) fault affecting the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Most often caused by loose, damaged or wrong fuel cap, saturated or damaged charcoal canister, faulty purge valve (canister purge solenoid).
P2406 — OBD2 code P2406 flags a problem with the evaporative emission (EVAP) system (evaporative emission system leak detection pump sense circuit high). The car is usually drivable while you plan the repair. Common culprits: faulty purge valve (canister purge solenoid), loose, damaged or wrong fuel cap, small leak in the fuel tank or filler neck.
P2407 — P2407 — Evaporative Emission System Leak Detection Pump Sense Circuit Intermittent/Erratic. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: cracked EVAP hoses or lines, saturated or damaged charcoal canister, loose, damaged or wrong fuel cap.
P2408 — Fuel Cap Sensor/Switch Circuit (P2408): a powertrain (engine/transmission) fault affecting the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Most often caused by saturated or damaged charcoal canister, cracked EVAP hoses or lines, loose, damaged or wrong fuel cap.
P2409 — OBD2 code P2409 flags a problem with the evaporative emission (EVAP) system (fuel cap sensor/switch circuit range/performance). The car is usually drivable while you plan the repair. Common culprits: saturated or damaged charcoal canister, small leak in the fuel tank or filler neck, faulty vent valve or leak detection pump.
P240B — Evaporative Emission System Leak Detection Pump Heater Control Circuit Low (P240B): a powertrain (engine/transmission) fault affecting the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Most often caused by cracked EVAP hoses or lines, saturated or damaged charcoal canister, faulty vent valve or leak detection pump.
P240C — P240C — Evaporative Emission System Leak Detection Pump Heater Control Circuit High. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: faulty purge valve (canister purge solenoid), saturated or damaged charcoal canister, small leak in the fuel tank or filler neck.
P2410 — Fuel Cap Sensor/Switch Circuit Low (P2410): a powertrain (engine/transmission) fault affecting the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Most often caused by loose, damaged or wrong fuel cap, small leak in the fuel tank or filler neck, saturated or damaged charcoal canister.
P2411 — P2411 — Fuel Cap Sensor/Switch Circuit High. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: loose, damaged or wrong fuel cap, small leak in the fuel tank or filler neck, faulty purge valve (canister purge solenoid).
P2412 — P2412 — Fuel Cap Sensor/Switch Circuit Intermittent/Erratic. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: small leak in the fuel tank or filler neck, faulty vent valve or leak detection pump, loose, damaged or wrong fuel cap.
P2413 — Exhaust Gas Recirculation System Performance (P2413): a powertrain (engine/transmission) fault affecting the exhaust gas recirculation (EGR) system. The car is usually drivable while you plan the repair. Most often caused by ECM control circuit fault, faulty EGR solenoid or wiring, failed EGR valve or position sensor.
P2414 — OBD2 code P2414 flags a problem with the oxygen sensor circuit (O2 sensor exhaust sample error bank 1 sensor 1). The car is usually drivable while you plan the repair. Common culprits: damaged sensor wiring or connector, ECM signal circuit fault, oil or coolant contamination of the sensor tip.
P2415 — OBD2 code P2415 flags a problem with the oxygen sensor circuit (O2 sensor exhaust sample error bank 2 sensor 1). The car is usually drivable while you plan the repair. Common culprits: blown sensor heater fuse, ECM signal circuit fault, damaged sensor wiring or connector.
P2416 — OBD2 code P2416 flags a problem with the oxygen sensor circuit (O2 sensor signals swapped bank 1 sensor 2/bank 1 sensor 3). The car is usually drivable while you plan the repair. Common culprits: oil or coolant contamination of the sensor tip, exhaust leak near the sensor, blown sensor heater fuse.
P2417 — P2417 — O2 Sensor Signals Swapped Bank 2 Sensor 2/Bank 2 Sensor 3. 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, exhaust leak near the sensor.
P2418 — P2418 — Evaporative Emission System Switching Valve Control Circuit/Open. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: faulty vent valve or leak detection pump, faulty purge valve (canister purge solenoid), cracked EVAP hoses or lines.
P2419 — Evaporative Emission System Switching Valve Control Circuit Low (P2419): a powertrain (engine/transmission) fault affecting the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Most often caused by faulty purge valve (canister purge solenoid), faulty vent valve or leak detection pump, cracked EVAP hoses or lines.
P2420 — P2420 — Evaporative Emission System Switching Valve Control Circuit High. A fault in the evaporative emission (EVAP) system. The car is usually drivable while you plan the repair. Typical causes: saturated or damaged charcoal canister, faulty purge valve (canister purge solenoid), cracked EVAP hoses or lines.
P2421 — OBD2 code P2421 flags a problem with the evaporative emission (EVAP) system (evaporative emission system vent valve stuck open). The car is usually drivable while you plan the repair. Common culprits: loose, damaged or wrong fuel cap, faulty vent valve or leak detection pump, faulty purge valve (canister purge solenoid).