Coolant Thermostat Below Regulating Temperature
The engine has been running long enough to reach operating temperature, but coolant temperature stayed below the thermostat's regulating value. Almost always caused by a thermostat stuck open. Costs fuel economy and increases cold-engine emissions.
Affected components
- Thermostat
- Coolant temperature sensor
Common causes
- High likelihood: Thermostat stuck open
- Low likelihood: Coolant sensor reading low
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
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.