Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
The thermostat is a valve that keeps the coolant hot until the engine reaches its working temperature. This code means the engine takes too long to warm up or doesn't reach that temperature.
What the car has detected
After several minutes of running, the coolant temperature is still below the level the thermostat should hold. It is usually stored when this happens on two trips in a row.
It is not dangerous in the short term, but the engine uses more fuel, the heater is weaker and some emissions checks don't complete. If the coolant level is also dropping, have it checked now.
Symptoms
- Engine warning light on
- The temperature gauge barely rises or takes a long time
- The heater blows only lukewarm air
- Higher fuel consumption
Possible causes
- Thermostat stuck open (the most common cause)
- Low coolant level
- Coolant temperature sensor reading too low
- Faulty intake air temperature sensor (the engine computer uses it in its calculations)
- Radiator fan that never switches off
- Water pump or heater valve not working properly
Checks for the garage
- Check the coolant level and look for leaks first
- Compare coolant, intake air and ambient temperatures with the engine cold: they should be similar
- Confirm the radiator fan switches off when it should
- Measure the coolant temperature sensor's resistance at different temperatures
- Test the thermostat and check the temperature at which it opens
- Clear the code and do two trips to confirm the repair
Next step
Check the coolant level with the engine cold and have the thermostat and engine temperature sensor checked.
Go to a garage if the coolant level is fine and the code comes back: replacing the thermostat usually means draining the system. If you are losing coolant or the gauge climbs too high, go as soon as possible.