P0125 — Insufficient Coolant Temperature for Closed-Loop Fuel Control
Drive with caution — fix soon.
What P0125 means
This code means the engine isn't reaching the temperature it needs to switch into closed-loop fuel control, where the computer uses oxygen sensor data to fine-tune fueling. Until that happens, the engine runs richer and less efficiently. The most common cause is a thermostat stuck open or a faulty coolant temperature sensor.
Common symptoms
- Check Engine light is on
- Engine takes a long time to warm up
- Poor fuel economy
- Heater blowing lukewarm air
- Temperature gauge staying below normal
Common causes
- Thermostat stuck open
- Faulty engine coolant temperature sensor
- Low coolant level
- Wiring or connector issues at the temp sensor
- Wrong thermostat installed previously
- Cooling fan running when it shouldn't
Typical repair cost
$100 – $350
Varies by vehicle and root cause.
Frequently asked questions
Can I drive with a P0125 code?
Usually yes, but expect worse fuel economy and a weak heater. It's not an emergency, though a stuck-open thermostat should be replaced soon to restore proper operation.
How much does it cost to fix P0125?
Often $100 to $350, depending on the cause. Replacing a thermostat is moderate; a sensor swap can be cheaper, while harder-to-reach parts cost more in labor.
Is P0125 serious?
It's a moderate concern. The car still runs, but staying out of closed-loop wastes fuel and increases emissions, so it's worth fixing.
Why won't my engine warm up with P0125?
Most often a thermostat is stuck open, letting coolant flow constantly so the engine never reaches operating temperature. A faulty temperature sensor can also trigger the code.