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

• P1771 — P1771 — Throttle High-Position Circuit Maximum Voltage. P1771 can affect idle stability and throttle response.
• P1772 — P1772 — Throttle Low-Position Minimum-Voltage Fault. P1772 can affect throttle-position sensing and may trigger reduced-power operation.
• P1773 — P1773 — Engine ECU–Additional Heater CAN Link. P1773 primarily affects communication with the additional heater rather than the engine's cooling system.
• P1774 — P1774 — Gear Shift Module CAN Communication Loss. P1774 can leave the gear shift module unreachable over CAN, making gear-position display or shifting unreliable.
• P1775 — OBD2 code P1775 flags a problem with the sensor and actuator circuits (timing solenoid circuit malfunction). The car is usually drivable while you plan the repair. Common culprits: control module driver fault, corroded, loose or damaged connector, open or shorted wiring in the circuit.
• P1776 — Torque Converter Clutch Circuit Malfunction (P1776): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by failed shift or pressure control solenoid, internal mechanical wear (clutches, torque converter), low or degraded transmission fluid.
• P1778 — OBD2 code P1778 flags a problem with the automatic transmission control (AG4 transmission torque modulation fault). Short, gentle driving to a shop is usually possible. Common culprits: wiring or connector faults in the valve body harness, low or degraded transmission fluid, valve body wear.
• P1779 — OBD2 code P1779 flags a problem with the sensor and actuator circuits (clutch solenoid circuit malfunction). 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.
• P1780 — Transmission System MIL Fault (P1780): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by failed shift or pressure control solenoid, faulty transmission speed sensor, low or degraded transmission fluid.
• P1781 — P1781 — Ignition Retard Request Duration Fault. 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, moisture or oil in the spark plug wells.
• P1782 — P1782 — Ignition Retard Request Circuit Fault. A fault in the ignition system. Short, gentle driving to a shop is usually possible. Typical causes: damaged coil wiring or connector, faulty ignition control circuit in the ECM, failed ignition coil or coil pack.
• P1783 — P1783 — Transmission Reverse I/P Circuit Malfunction. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: faulty transmission speed sensor, wiring or connector faults in the valve body harness, low or degraded transmission fluid.
• P1784 — OBD2 code P1784 flags a problem with the sensor and actuator circuits (TCIL circuit malfunction). The car is usually drivable while you plan the repair. Common culprits: open or shorted wiring in the circuit, corroded, loose or damaged connector, blown fuse feeding the circuit.
• P1785 — Trans Control Switch (O/D Cancel) Out of Self Test Range (P1785): 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, faulty sensor or actuator of the affected circuit.
• P1786 — 4X4 Switch Out of Self Test Range (P1786): 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, open or shorted wiring in the circuit.
• P1787 — P/ES Circuit Out Of Self Test Range (P1787): 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, corroded, loose or damaged connector.
• P1788 — P1788 — Transmission Overtemperature Condition. A fault in the engine cooling and temperature control. Short, gentle driving to a shop is usually possible. Typical causes: faulty coolant temperature sensor, low coolant level or air in the system, failed cooling fan or fan relay.
• P1789 — Transmission Mechanical Failure - First And Reverse (P1789): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by failed shift or pressure control solenoid, low or degraded transmission fluid, faulty transmission speed sensor.
• P1790 — OBD2 code P1790 flags a problem with the automatic transmission control (transmission mechanical failure - first and second). Short, gentle driving to a shop is usually possible. Common culprits: low or degraded transmission fluid, wiring or connector faults in the valve body harness, failed shift or pressure control solenoid.
• P1791 — 3-2 Downshift Error (P1791): 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, corroded, loose or damaged connector, faulty sensor or actuator of the affected circuit.
• P1792 — 2-1 Downshift Error (P1792): 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, poor ground connection, open or shorted wiring in the circuit.
• P1793 — P1793 — Pressure Control Solenoid "B" Open Circuit. A fault in the automatic transmission control. Short, gentle driving to a shop is usually possible. Typical causes: valve body wear, low or degraded transmission fluid, internal mechanical wear (clutches, torque converter).
• P1794 — Pressure Control Solenoid "B" Short Circuit (P1794): a powertrain (engine/transmission) fault affecting the automatic transmission control. Short, gentle driving to a shop is usually possible. Most often caused by low or degraded transmission fluid, failed shift or pressure control solenoid, internal mechanical wear (clutches, torque converter).
• P1795 — OBD2 code P1795 flags a problem with the sensor and actuator circuits (TP (Mechanical) circuit malfunction). The car is usually drivable while you plan the repair. Common culprits: control module driver fault, poor ground connection, open or shorted wiring in the circuit.