P0125 Code: Insufficient Coolant Temperature for Closed Loop Fuel Control
🟠 Moderate severity · drivable
You can drive, but the engine will run rich and use more fuel until it warms up properly.
What P0125 means
The engine takes too long to reach the temperature needed for closed loop fuel control, where the computer fine-tunes the fuel mixture using the oxygen sensors. The engine stays in open loop and runs rich. A stuck-open thermostat is the usual cause.
Symptoms
- Check engine light on
- Poor fuel economy
- Engine runs rich
- Long warm-up time
- Rough idle when cold
Common causes
- most common: Thermostat stuck open
- common: Faulty ECT sensor
- common: Low coolant level
- less common: Cooling fan running all the time
How to fix it
| Fix | DIY? | Typical cost |
|---|---|---|
| Replace the thermostat | Yes | $30–120 |
| Replace the ECT sensor | Yes | $20–80 |
| Top up coolant and fix leaks | Yes | $10–50 |
| Repair the cooling fan circuit | Mechanic | $150–400 |
Frequently asked questions
Can I drive with P0125?
Yes, but the engine will run rich and use more fuel until it warms up. Replace the thermostat if it is stuck open.
What is closed loop fuel control?
It is the mode where the computer fine-tunes the fuel mixture using oxygen sensor feedback after the engine warms up.
Will a new thermostat fix P0125?
In most cases, yes. A stuck-open thermostat is the most common cause of this code.
Related codes
P0116
P0116 Code: Engine Coolant Temperature Sensor Range/Performance
P0117P0117 Code: Engine Coolant Temperature Circuit Low Input
P0128P0128 Code: Coolant Thermostat (Coolant Temperature Below Regulating Temperature)
Updated 2026-08. This page is informational and not a substitute for professional diagnosis.