Cold Start Engine Coolant Temperature Performance
During cold-start the ECU expects coolant temperature to rise within a calibrated time window. Either the engine warms up too slowly (stuck-open thermostat, weak combustion) or the temperature signal does not reflect the actual warm-up.
Affected components
- Thermostat
- Coolant temperature sensor
Common causes
- High likelihood: Thermostat stuck open - engine warms too slowly
- Medium likelihood: Coolant temperature sensor drifts low
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
Sources
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.