P0125
Low SeverityInsufficient Coolant Temperature for Closed Loop Fuel Control
Cooling System
What Does P0125 Mean?
The engine is not reaching proper operating temperature for the fuel system to go into closed-loop mode. Typically a stuck-open thermostat.
Common Fix
Replace thermostat
Estimated Cost (DIY)
$15 - $40
Symptoms
- ⚠️Poor fuel economy
- ⚠️Heater blows lukewarm
- ⚠️Temperature gauge stays low
- ⚠️Check engine light
Common Causes
Stuck-open thermostatlikely
Faulty ECT sensorpossible
Missing or wrong thermostatpossible
How to Diagnose P0125
- 1Check if engine reaches operating temp (190-210°F)
- 2Compare ECT sensor reading to actual temp
- 3Inspect thermostat
- 4Replace thermostat if stuck open
Need to read or clear this code?
Shop OBD2 Scanners on Amazon →Ready to fix it yourself?
View Step-by-Step Repair Guide →Select your exact vehicle for a personalized guide
Frequently Asked Questions
- Is P0125 the same as P0128?
- Very similar. P0125 means the ECM cannot enter closed-loop fuel control. P0128 means the coolant has not reached expected temp within a time limit. Both usually mean a stuck thermostat.
- Can I drive with P0125?
- Yes, but fuel economy suffers and your heater will not work well in winter. Replace the thermostat soon.