DTC P0125: Insufficient Coolant Temp For Closed-Loop Fuel Control: Testing

WARNING: Never open the cooling system when the engine is hot. The system is under pressure. Extreme burns or scalding may result. Allow the engine to cool before opening the cooling system.

WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.

NOTE: If an ECT sensor DTC is also present, diagnose ECT sensor DTC first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . Ensure ECT sensor and related PCM harness connector terminals are free from corrosion and damage. For best results, allow vehicle to cool overnight before performing test. Extremely cold ambient temperatures may cause this DTC to set.

Check coolant level and condition. Is the coolant level and condition okay? If yes, go to next step. If no, check for coolant leak and add necessary amount of coolant.

NOTE: This test works best if performed on a cold engine (cold soak).

Ignition on, engine not running. With the DRBIII® scan tool, read the ECT Deg 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 180°F (82°C), allow the engine to cool until 150°F (65°C) is reached. Start the Engine. During engine warm-up, monitor the ECT Deg value. The Temp Deg Value change should be a smooth transition from start-up to normal operating temp 180°F (82°C). Also monitor the actual coolant temperature with a thermometer. As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the ECT Deg in the DRBIII® scan tool values should stay relatively close to each other. Thermostat should open at about 195°F (90°C). Did the thermostat open at the proper temperature? If yes, go to next step. If no, replace the thermostat.

NOTE: For this test to be valid, the thermostat must be operating correctly. This test works best if performed on a cold engine (cold soak).

Ignition on, engine not running. With the DRBIII® scan tool, read the ECT sensor temperature 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 180°F (82°C), allow the engine to cool until 150°F (65°C) is reached. Start the engine. During engine warm-up, monitor the ECT Deg value. The temp deg value change should be a smooth transition from start-up to normal operating temp 180°F (82°C). As the engine warms up to operating temperature, the actual coolant temperature (thermometer reading) and the ECT sensor temperature in the DRBIII® scan tool sensors should stay relatively close to each other. Is the thermometer reading relatively close to the DRBIII® scan tool ECT sensor reading? If yes, test is complete. If no, replace the engine coolant temperature sensor.