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Generic gasoline powertrain DTC / Engine temperature management

P0118: Engine coolant temperature circuit high input

The controller detected a high input in the engine coolant temperature circuit.

Generic definition
P0117
P0128

Likely cause paths · unconfirmed

A possible temperature sensor or circuit issue

The reported temperature may be affected by the sensor circuit or connection; the code alone does not prove the sensor is faulty.

  • Note whether the gauge or warning changes suddenly.
  • Record other temperature or circuit codes.

A possible cooling or temperature-regulation issue

Coolant level, flow, air in the system, or temperature regulation may affect the monitor. The safe test depends on the vehicle.

  • Only when fully cold, look for visible coolant loss without opening a pressurized system.
  • Record recent cooling-system work and any overheating history.

Likely causes and repair directions are general, conditional orientation. The SAE citation supports the generic DTC definition only; it does not validate these causes, tests, repairs, or fitment to a particular vehicle.

Conditional likely repairs

A code describes a monitored condition; it does not prove a failed part. Use these directions only after confirming the cause.

If confirmed: A possible temperature sensor or circuit issue

If circuit diagnosis confirms an electrical or sensor fault, repair the verified circuit or component using the OEM test procedure.

Evidence to confirm

  • Circuit checks isolate the fault.
  • Cold-soak and operating scan readings agree with the vehicle-specific reference after repair.

If confirmed: A possible cooling or temperature-regulation issue

If cooling-system testing confirms a leak, flow, or regulation problem, repair that verified cause and follow the OEM fill and bleed procedure.

Evidence to confirm

  • A cold inspection or pressure/flow test identifies the condition.
  • The system holds coolant and the temperature monitor completes normally.

Guided evidence checks

  1. 01

    Record what happened

    Note when the warning appeared, what the vehicle was doing, and any recent service or change. Do not deliberately recreate an unsafe symptom.

  2. 02

    Make only a safe visual check

    From a safe position, note the gauge, warning message, visible steam, or coolant on the ground. Never open a hot cooling system.

  3. 03

    Preserve scan-tool evidence

    Qualified technician

    Save code status, freeze-frame, and displayed coolant-temperature data; do not use a generic pass/fail temperature.

  4. 04

    Confirm the system path

    Qualified technician

    A qualified technician should compare a cold-soak reading, sensor circuit, coolant condition, and temperature-regulation operation with OEM information.

Code-specific symptom note

  • Code-specific symptoms are not verified by the cited definition. Record the driver’s actual observations separately.

This generic code reference is not an OEM procedure, does not confirm that a DTC applies to a particular make/model/engine, and is not a repair diagnosis. Follow vehicle-specific service information or consult a qualified technician.