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.
Coolant Temp Sensor Description

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