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

• P1131 — Throttle Position (Narrow Range) Sensor Circuit Malfunction (P1131): a powertrain (engine/transmission) fault affecting the throttle and intake air metering. Short, gentle driving to a shop is usually possible. Most often caused by intake air leaks after the MAF sensor, contaminated or failed MAF/MAP sensor, wiring or connector faults in the throttle circuit.
• P1133 — P1133 — Upstream Heated O2 Sensors Swapped. A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: blown sensor heater fuse, aged or contaminated oxygen sensor, oil or coolant contamination of the sensor tip.
• P1134 — Downstream Heated O2 Sensors Swapped (P1134): 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, exhaust leak near the sensor, damaged sensor wiring or connector.
• P1136 — OBD2 code P1136 flags a problem with the oxygen sensor circuit (lack of HO2S switch - sensor indicates lean). The car is usually drivable while you plan the repair. Common culprits: damaged sensor wiring or connector, oil or coolant contamination of the sensor tip, exhaust leak near the sensor.
• P1137 — Lack Of HO2S Switch - Sensor Indicates Rich (P1137): 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, damaged sensor wiring or connector, oil or coolant contamination of the sensor tip.
• P1138 — OBD2 code P1138 flags a problem with the oxygen sensor circuit (HO2S insufficient switching sensor 1). The car is usually drivable while you plan the repair. Common culprits: aged or contaminated oxygen sensor, damaged sensor wiring or connector, ECM signal circuit fault.
• P1139 — HO2S Transition Time Ratio Sensor 1 (P1139): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by damaged sensor wiring or connector, aged or contaminated oxygen sensor, exhaust leak near the sensor.
• P1140 — Pedal Position Sensor A Circuit Intermittent (P1140): 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, control module driver fault, poor ground connection.
• P1141 — Fan Control Circuit Malfunction (P1141): 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, open or shorted wiring in the circuit, control module driver fault.
• P1142 — OBD2 code P1142 flags a problem with the oxygen sensor circuit (lack of HO2S switch - sensor indicates lean). 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.
• P1143 — Lack Of HO2S12 Switch - Sensor Indicates Rich (P1143): a powertrain (engine/transmission) fault affecting the oxygen sensor circuit. The car is usually drivable while you plan the repair. Most often caused by damaged sensor wiring or connector, oil or coolant contamination of the sensor tip, exhaust leak near the sensor.
• P1144 — P1144 — Water In Fuel Indicator Circuit Malfunction. 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.
• P1145 — P1145 — Calculated Engine Torque Mismatch. P1145 indicates that the controller cannot reconcile commanded and calculated torque, which can cause poor response, surging, or limp-mode operation.
• P1146 — P1146 — Alternator Load Input Too High. P1146 warrants prompt inspection because continued operation with genuinely excessive charging voltage can damage the battery, wiring, and electronic modules.
• P1148 — P1148 — Alternator Control Circuit 2 Malfunction. P1148 can interrupt alternator control and leave the battery charging poorly.
• P1149 — P1149 — Alternator Control Circuit 2 Overvoltage. P1149 indicates excessive voltage in alternator control circuit 2.
• P1150 — P1150 — Water In Fuel Condition. 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, poor ground connection, control module driver fault.
• P1151 — Fuel Restriction Indicator Circuit Malfunction (P1151): 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, faulty sensor or actuator of the affected circuit, corroded, loose or damaged connector.
• P1153 — OBD2 code P1153 flags a problem with the sensor and actuator circuits (air assist control valve range/performance). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, faulty sensor or actuator of the affected circuit, blown fuse feeding the circuit.
• P1154 — P1154 — Air Assist Control Valve Circuit Malfunction. 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, poor ground connection, control module driver fault.
• P1155 — OBD2 code P1155 flags a problem with the oxygen sensor circuit (lack of HO2S21 switch - adaptive fuel at limit). The car is usually drivable while you plan the repair. Common culprits: blown sensor heater fuse, aged or contaminated oxygen sensor, oil or coolant contamination of the sensor tip.
• P1157 — P1157 — Lack Of HO2S21 Switch - Sensor Indicates Rich. A fault in the oxygen sensor circuit. The car is usually drivable while you plan the repair. Typical causes: ECM signal circuit fault, oil or coolant contamination of the sensor tip, damaged sensor wiring or connector.
• P1158 — Bank 2 Fuel Control Shifted Lean (P1158): 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.
• P1159 — Bank 2 Fuel Control Shifted Rich (P1159): 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.