P0125
Insufficient Coolant Temperature for Closed Loop Fuel Control
The engine has run long enough that closed-loop fuel control should be active, but the coolant temperature has not risen high enough. Often caused by a stuck-open thermostat or a failed coolant temperature sensor.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Thermostat stuck openCommon
- Coolant temp sensor reading lowPossible
Parts involved
- Thermostat
- Coolant Temperature Sensor
P0125 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.