P0118 — Engine Coolant Temperature Sensor High Input
The ECT signal voltage is above threshold, which the ECU interprets as an implausibly cold temperature (open-circuit-like behaviour). When this code is active, the ECU runs a default cold-start enrichment that wastes fuel and may cause black smoke.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Coolant temperature sensor
- Coolant temperature sensor wiring
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Open circuit in sensor or wiring
- Corroded sensor connector
Possible symptoms
- Check engine light on
- Cooling fan runs constantly or not at all
- Cabin heater weak or excessively hot
- Possible long warm-up time or hard cold start
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
Sources
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.