The engine stays below its normal regulating temperature. The driver may notice a low temperature gauge, weak cabin heat and higher consumption.
Likely causes, most common first
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant level
- Cooling fan running all the time
Parts usually involved
- Thermostat
- Coolant temperature sensor
Test before you replace
Watch live coolant temperature on a road test and check that the upper hose stays cool until the thermostat opens.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.