P0125 means Insufficient Coolant Temperature for Closed Loop Fuel Control. The engine is taking too long to reach the temperature the computer needs before it starts using oxygen sensor feedback for fuel control. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0125 means
The coolant temperature reading feeds many systems: warm-up fueling, ignition timing, idle speed, cooling fan control, transmission shift timing and often the dash gauge. A wrong reading causes symptoms far beyond the cooling system, and a real overheat can damage an engine quickly. Confirm the actual temperature with a scan tool or an infrared thermometer before replacing parts.
P0125 symptoms
- Check engine light
- Slow warm-up and weak cabin heat
- Higher fuel consumption
Common causes of P0125
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant
How to diagnose P0125
- Watch coolant temperature from a cold start
- Check the coolant level
- Test or replace the thermostat if warm-up is slow
Can you drive with P0125?
Yes, but fuel economy and heater output suffer until it is fixed.
P0125 tips
P0125 and P0128 often appear together with a weak thermostat; replacing the thermostat with the correct temperature rating fixes both. Very cold weather and long idling can make a borderline thermostat set the code, so note the conditions when it appeared.
Will P0125 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0125 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0128 | Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) |
| P0116 | Engine Coolant Temperature Circuit Range/Performance |
| P0117 | Engine Coolant Temperature Sensor 1 Circuit Low |
Guides that help
When it is more than a sensor
Most cooling codes end with a thermostat, sensor, fan or leak repair. If the engine overheated badly enough to fail the head gasket or warp the heads, compare a repair against a replacement on our engines page and read engine replacement cost.
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