All trouble codes → Coolant temperature & thermostat codes
Coolant temperature & thermostat codes
These codes set when the engine warms up too slowly or never reaches operating temperature — most often a thermostat stuck open, a coolant temperature sensor reading low, or a low coolant level. Watching the temperature climb from a cold start tells you quickly whether the thermostat or the sensor is at fault.
Diagnose before extended driving.
Common causes
- Thermostat stuck open
- Coolant temperature sensor reading low
- Low coolant level
First checks
- Watch ECT from a cold start: it should rise steadily to ~85–105 °C (185–220 °F) and stabilise
- Compare ECT with IAT/ambient after an overnight cold soak — they should match within a few degrees
System: Fuel & air metering. This is general guidance for the generic OBD-II codes in this group; always confirm against the service information for your specific vehicle.
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