Fault-Code Library · Cooling system
P0118: Engine coolant temperature sensor circuit high
The coolant-temperature signal is implausibly high voltage, often read by the ECU as extremely cold coolant.
Common symptoms
- •Hard starting
- •Rich running
- •Cooling fan behavior changes
- •Temperature reading implausible
Likely causes
- •Open circuit in coolant sensor wiring
- •Failed coolant temperature sensor
- •Connector corrosion
- •Incorrect sensor data after repair
First checks
- •Compare coolant temperature to ambient before startup
- •Inspect the sensor connector and wiring
- •Check live data while moving the harness
Important
Bad temperature data can affect fueling, fan control, warm-up strategy, and emissions readiness.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
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