Circuit Description
The coolant temperature sensor is a thermister. The 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 DIM over the Class 2
serial data circuit. The DIM will not request A/C compressor clutch engagement if
the engine coolant temperature is high. If the PCM determines that a fault is present
in the coolant temp 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 disables the A/C clutch.
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 compressor 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
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, test the
following conditions 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 |
| • | Current or history engine coolant temperature sensor DTCs in the PCM |
| • | Trailer weight exceeding 454 kg (1000 lb) in extreme high
ambient temperatures |
| • | Aftermarket products affecting cooling system performance |
