Engine Coolant Temp Sensor Operation And Description

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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How Things Work