The engine coolant temperature (ECT) sensor is a variable resistor that measures the
temperature of the engine coolant. The powertrain control module (PCM) supplies 5 volts to the
signal circuit. When coolant temperatures are low, resistance is high. When coolant
temperatures are high the resistance is low.

The PCM uses this input for engine controls and enabling criteria for diagnostics. The PCM will
record the amount of time the engine is OFF. At restart the PCM will compare the temperature
difference between the ECT and intake air temperature (IAT). If the temperature difference is not
within the calculated amount, after the predetermined soak time, this DTC will set.
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Coolant Temp Sensor Operation And Description