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

    NOTE: If an ECT DTC is also set with this code, diagnose the ECT DTC first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . Inspect the ECT terminals and related PCM terminals. Ensure the terminals are free from corrosion and damage. The best way to diagnose this DTC is to allow the vehicle to sit overnight outside in order to have a totally cold soaked engine. Extremely cold outside ambient temperatures may have caused this DTC to set.
    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.
  1. Check the cooling system to make sure that the coolant is in good condition and at the proper level. Is the coolant level and condition okay? If yes, go to next step. If no, inspect the vehicle for a coolant leak and add the necessary amount of coolant.
    2. NOTE: This test works best if performed on a cold engine (cold soak).
  2. Turn ignition on, engine not running. With the DRBIII®, read the Eng Coolant Tmp 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 Eng Coolant Tmp 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 Eng Coolant Tmp Deg in the DRBIII® 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.
  3. Turn ignition on, engine not running. With the DRBIII®, read the Eng Coolant Tmp 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 Eng Coolant Tmp 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 Eng Coolant Tmp Deg in the DRBIII® values should stay relatively close to each other. Is the thermometer reading relatively close to the DRBIII® ECT reading? If yes, test is complete. If no, replace the Engine Coolant Temperature Sensor.
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