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

• P0154 — OBD2 code P0154 flags a problem with the sensor and actuator circuits (02 sensor circuit no activity detected (bank 2 sensor 1)). 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, corroded, loose or damaged connector.
• P0155 — 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1) (P0155): 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.
• P0156 — P0156 — 02 Sensor Circuit Malfunction (Bank 2 Sensor 2). A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: control module driver fault, corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit.
• P0157 — P0157 — 02 Sensor Circuit Low Voltage (Bank 2 Sensor 2). 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, control module driver fault, corroded, loose or damaged connector.
• P0158 — 02 Sensor Circuit High Voltage (Bank 2 Sensor 2) (P0158): 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.
• P0159 — 02 Sensor Circuit Slow Response (Bank 2 Sensor 2) (P0159): 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, control module driver fault, open or shorted wiring in the circuit.
• P015A — O2 Sensor Delayed Response - Rich to Lean (Bank 1 Sensor 1) (P015A): 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, blown sensor heater fuse, damaged sensor wiring or connector.
• P015B — P015B — O2 Sensor Delayed Response - Lean to Rich (Bank 1 Sensor 1). A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: blown sensor heater fuse, ECM signal circuit fault, oil or coolant contamination of the sensor tip.
• P015C — O2 Sensor Delayed Response - Rich to Lean (Bank 2 Sensor 1) (P015C): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by exhaust leak near the sensor, ECM signal circuit fault, aged or contaminated oxygen sensor.
• P015D — P015D — O2 Sensor Delayed Response - Lean to Rich (Bank 2 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, damaged sensor wiring or connector, oil or coolant contamination of the sensor tip.
• P0160 — P0160 — 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 2). A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: poor ground connection, corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit.
• P0161 — P0161 — 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2). 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.
• P0162 — 02 Sensor Circuit Malfunction (Bank 2 Sensor 3) (P0162): 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, blown fuse feeding the circuit, open or shorted wiring in the circuit.
• P0163 — P0163 — 02 Sensor Circuit Low Voltage (Bank 2 Sensor 3). 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, blown fuse feeding the circuit.
• P0164 — 02 Sensor Circuit High Voltage (Bank 2 Sensor 3) (P0164): 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, corroded, loose or damaged connector.
• P0165 — OBD2 code P0165 flags a problem with the sensor and actuator circuits (02 sensor circuit slow response (bank 2 sensor 3)). The car is usually drivable while you plan the repair. Common culprits: control module driver fault, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.
• P0166 — 02 Sensor Circuit No Activity Detected (Bank 2 Sensor 3) (P0166): 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, faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit.
• P0167 — P0167 — 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 3). 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, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.
• P0168 — P0168 — Fuel Temperature Too High. 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.
• P0169 — Incorrect Fuel Composition (P0169): 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, corroded, loose or damaged connector, open or shorted wiring in the circuit.
• P0170 — P0170 — Fuel Trim Malfunction (Bank 1). A fault in the fuel delivery and mixture control. Short, gentle driving to a shop is usually possible. Typical causes: faulty fuel pressure regulator, vacuum or intake leaks skewing the mixture, faulty fuel rail pressure sensor or wiring.
• P0171 — P0171 — System too Lean (Bank 1). 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, corroded, loose or damaged connector, blown fuse feeding the circuit.
• P0172 — P0172 — System too Rich (Bank 1). 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, faulty sensor or actuator of the affected circuit.
• P0173 — P0173 — Fuel Trim Malfunction (Bank 2). A fault in the fuel delivery and mixture control. Short, gentle driving to a shop is usually possible. Typical causes: vacuum or intake leaks skewing the mixture, faulty fuel rail pressure sensor or wiring, faulty fuel pressure regulator.