P0118 Engine Coolant Temperature Circuit High

P0118 indicates a high engine-coolant-temperature circuit input. The module may be seeing an implausibly cold coolant value because the circuit is open or has excessive resistance.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace cooling parts only because the engine seems to run rich or the fan behaves oddly; first prove the temperature signal is valid.

Symptoms of P0118

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0118

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Compare coolant temperature, intake-air temperature, and ambient temperature after a cold soak.
Inspect coolant-temperature sensor wiring, connector terminals, sensor ground, and coolant contamination at the connector.
Check whether fans, enrichment, or temperature-gauge behavior match the scan-tool reading.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.