Cooling system
P0125 — Insufficient Coolant Temperature for Closed Loop Fuel Control
The engine is taking too long to reach the temperature needed for closed-loop fuel control. Until then, the ECU keeps enriching the mixture, which wastes fuel and increases emissions.
Common causes
- Thermostat stuck open
- Faulty coolant temperature sensor
- Low coolant level
- Cooling fan running constantly
- Faulty oxygen sensor heater
Symptoms
- Heater blows lukewarm air
- Temperature gauge stays low
- Higher fuel consumption
- Check engine light
How to check
- Check the coolant level
- Watch the ECT value while warming up and compare it with a real thermometer
- Check the thermostat operation
- Check fan operation and the oxygen sensor heater circuit
Can you keep driving?
Usually safe to drive, but fuel consumption rises and the heater is weak. Repair at your convenience.
Related codes
Frequently asked questions
- What does P0125 mean?
- The engine does not warm up fast enough for the ECU to switch to closed-loop fuel control.
- Is a thermostat the usual cause?
- Yes, a thermostat stuck open is the most common cause.
General reference information. It does not replace a diagnosis on your own vehicle. The same code can have different causes depending on make, model year and engine; check the manufacturer's documentation or ask a technician with a scan tool.