Circuit Description
The powertrain control module (PCM) monitors the engine coolant temperature through the engine coolant temperature (ECT) 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 serial data circuit. 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 coolant temperature sensor circuit it will set DTC P0117 or P0118 and use a default coolant temperature value. This value is then sent from the PCM to the DIM over the class 2 serial data circuit.
Conditions for Running the DTC
The DIM must be powered.
Conditions for Setting the DTC
The engine coolant temperature is equal to or greater than 121°C (250°F) for more than 2 seconds.
Action Taken When the DTC Sets
The DIM will not request the A/C clutch ON.
Conditions for Clearing the DTC
| • | When the engine coolant temperature drops to less than 119°C (246°F) the DIM will clear the current DTC and go to a history DTC. If A/C is still requested, the DIM will then enable the A/C clutch. |
| • | The history DTC will clear after 40 ignition cycles. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
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 clutch 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:
| • | Inoperative engine cooling fans |
| • | Debris in front of the A/C condenser |
| • | Radiator or A/C condenser air shields missing or out of location |
| • | Low coolant level |
| • | Inoperative thermostat |
| • | Water pump failure |
| • | Check the PCM for current or history engine coolant temperature sensor DTCs. |
| • | Trailer weight exceeding 454 kg (1000 lb) in extreme high ambient temperatures |
| • | Aftermarket products affecting cooling system performance |
Step | Action | Yes | No |
|---|---|---|---|
1 | Was the Diagnostic System Check for Engine Cooling performed? | Go to Step 2 | Go to Diagnostic System Check - Engine Cooling in Engine Cooling |
2 | Check the engine cooling fans for proper operation. Are the engine cooling fans operative? | Go to Engine Overheating in Engine Cooling | Go to Symptoms - Engine Cooling in Engine Cooling |
