Circuit Description
The 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 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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1540 Air Conditioning (A/C) Refrigerant Over Pressure - A/C
Disabled
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 |
