Insufficient Coolant Temperature for Closed Loop Fuel Control
The engine has been running long enough that it should be in closed-loop fuel control, but the ECU never sees the coolant reach the expected temperature. Almost always a thermostat that is stuck open.
Indication de gravité : Faible — généralement sans impact sur la conduite, à traiter à la prochaine révision
Symptômes que vous remarquerez
- Heater blows lukewarm
- Temperature gauge below normal
- Higher fuel consumption
- Emissions test failure
Causes fréquentes
Classées du plus au moins probable — commencez en haut.
- 1 Thermostat stuck open
- 2 Failed coolant temperature sensor reading low
- 3 Very cold ambient use with a short journey cycle
Comment le diagnostiquer
Le moins cher et le moins invasif d'abord — la plupart de ces codes ne sont pas un problème de pièces.
- ✓ Watch ECT on a scan tool during a 10-minute drive; it should stabilise around 85–95 °C.
- ✓ Feel the upper and lower radiator hoses — both getting warm early means the thermostat is open.
- ✓ Compare ECT with a infrared thermometer on the housing.
Options de réparation
- Replace the thermostat
- Replace the ECT sensor if it reads implausibly low
- Bleed the cooling system
P0125 — questions fréquentes
Is this urgent? +
Not mechanically urgent, but running rich long-term damages the catalytic converter and washes oil films off cylinder walls.
Could it just be a cold day? +
In sub-zero conditions with short trips, yes — confirm with a longer drive before replacing parts.
Confirmez le diagnostic avant d'acheter des pièces
Envoyez-nous le code, les données figées et le véhicule — nos ingénieurs vous diront quoi tester en premier.