P0125
ECT Insufficient for Closed-Loop Fuel Control
low
i Description
The engine has not reached a sufficient temperature for the ECU to enter closed-loop fuel control within the expected time. In open-loop, the engine runs richer, increasing emissions and fuel consumption.
? Common Causes
- Stuck-open thermostat
- Faulty ECT sensor
- Low coolant level
- Extremely cold ambient conditions
! Symptoms
- Check engine light
- Poor fuel economy
- Engine slow to warm up
- Weak heater output
# Diagnostic Steps
- Check thermostat — engine should reach ~80°C within 10 minutes
- Test ECT sensor readings
- Verify coolant level
- Compare ECT to IAT at cold start
⚙ Typical Fix
Replace the thermostat.
Parts Needed
Thermostat, Coolant
Estimated Cost
$50-$200
↔ Related Codes
Q Frequently Asked Questions
Yes. The engine will just take longer to warm up and use more fuel. Replace the thermostat when convenient.
☞ Learn More
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