The engine coolant temperature sensor is a thermister. The powertrain control module (PCM) determines the temperature of the engine coolant based on the voltage from the sensor. When the sensor is cold, its resistance and voltage are high. When the sensor is warm, its resistance and voltage are low. The PCM sends the coolant temperature data to the dash integration module (DIM) over the Class 2 communication line. The DIM will not request A/C compressor clutch engagement if the engine coolant temperature is too high. If the PCM determines that a fault is present in the ECT sensor signal circuit it will set DTC P0117 or P0118 and substitute a default coolant temperature value. This value is then sent from the PCM to the DIM over the Class 2 communication line.

The DIM must be powered.

The engine coolant temperature is equal to or greater than 121°C (250°F) for more than 2 seconds.

The DIM disables the A/C compressor clutch.

If DTC P1536 is stored as a history code it indicates that the DIM did receive a high engine coolant temperature message from the PCM. Interrupting A/C compressor operation can occur as a normal function to protect the engine from overheating, as when pulling a trailer up a hill. If the condition occurs frequently, check the following for a possible cause: