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DTC P0125: Closed Loop Temperature Not Reached: Testing

NOTE: If an ECT sensor DTC is also present, diagnose ECT sensor DTC first. 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.
WARNING: DO NOT open cooling system when engine is hot.
  1. Check coolant level and condition. If coolant level and condition are okay, go to next step. If coolant level or condition is not okay, check for coolant leak and add necessary amount of coolant.
  2. Turn ignition on. Using scan tool, read engine coolant temperature. If vehicle was allowed to cool overnight, engine coolant temperature should be close to ambient temperature. If engine coolant temperature is more than 180°F (82°C), allow engine to cool until 150°F (66°C) is reached. Start engine. Monitor engine coolant temperature on scan tool while engine is warming up. Engine coolant temperature should increase smoothly to normal operating temperature. Thermostat should stay closed until engine coolant temperature reaches 192-199°F (89-93°C). Replace thermostat, if operation is not as specified. If no problems are found, test is complete.
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