P0125 Insufficient Coolant Temp for Closed-Loop fuel control

P0125 Insufficient Coolant Temp for Closed-Loop fuel control - at initial engine start up, with battery voltage greater than 10.4 volts. Set conditions, the engine temperature does not go above 10°C (50°F). Failure time depends on start up coolant temperature and ambient temperature: Up two minutes for a start temp of 1°C (33.8°F) or above, up to five minutes for a vehicle with a start-up temp between 0°C and -29°C (32°F and-20.2°F), up to 10 minutes for a vehicle with a start-up temp of -30°C (-22°F) or below. Default action this code the MIL light will illuminate.

P0125-Insufficient Coolant Temp for Closed-Loop fuel control

Possible causes P0125 code:
  • Low coolant level.
  • Coolant system issues
  • Thermostat.
  • Engine Coolant Temperature (ECT) sensor.

Diagnose code P0125-Insufficient Coolant Temp for Closed-Loop fuel control

Step 1. Check the coolant level and condition

Warning : Never open the cooling system when the engine is hot. The system is under pressure. Extreme burns or scalding may result. Failure to follow these instructions can result in possible serious or fatal injury. Allow the engine cool before opening the cooling system.

Inspect the cooling system for proper level and condition.

Is the coolant level and condition OK?

Yes, go to step 2.
No, Inspect the vehicle for a leak, make the appropriate repair and add the correct amount of coolant.

Step 2. Thermostat Operation
The best way to diagnose this DTC is to allow the vehicle to sit overnight outside in order to start the test with a totally cold soaked engine. Turn the ignition on, with the scan tool, read the Engine Coolant Temperature degree value. If the engine was allowed to sit overnight (cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature. If engine coolant temperature is above 82°C (180°F), allow the engine to cool until 65°C (150°F) is reached.
Start the engine. During engine warm-up monitor the Engine Coolant Temperature degree value. The temperature value change should be a smooth transition from start up to normal operating temp 82°C (180°F). Also monitor the actual coolant temperature with a digital thermometer at or near the ECT sensor and Thermostat positions.
As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the scan tool Engine Coolant Temperature degree values should stay relatively close to each other. Using the appropriate service information, determine the proper opening temperature of the thermostat.

Did the thermostat open at the proper temperature?

Yes, go to step 3.
No, replace the thermostat.

Step 3. ECT Sensor operation

Was the digital thermometer readings relatively close to the scan tool reading for the ECT Sensor?

Yes, go to step 4.
No, replace the Engine Coolant Temperature (ECT) Sensor.

Step 4. Cooling System operation
Check the temperature reading at the inlet and outlet of the Radiator. It is normal to see a lower temperature on the outlet of the Radiator, however a very large difference indicates a restriction in the Radiator core. This can cause this DTC to set due to the position on the ETC Sensor in the system.

Where the difference in the temperature readings relatively larger than expected?

Yes, replace the Radiator.
No, go to step 5.

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