DTC P0125: Insufficient Engine Coolant Temperature For Closed Loop Fuel Control: Description
CAUTION:
Do not use ECM ground terminals when measuring input/output voltage. Doing so may result in damage to the ECM's transistor. Use a ground other than ECM terminals, such as the ground.
The Engine Coolant Temperature (ECT) sensor is used to detect the engine coolant temperature. See Figure. The sensor modifies a voltage signal from the ECM. The modified signal returns to the ECM as the engine coolant temperature input. The sensor uses a thermistor which is sensitive to the change in temperature. The electrical resistance of the thermistor decreases as temperature increases. See Figure and ECT VOLTAGE & RESISTANCE table.