Circuit Description
The powertrain control module (PCM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the PCM commands the cooling fans on. When pressure is too high or too low, the PCM will not allow the A/C compressor clutch to engage. The PCM sends the A/C pressure 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 A/C pressure is too high.
Conditions for Running the DTC
The DIM must be powered.
Conditions for Setting the DTC
The A/C refrigerant pressure is greater than 2968 kPa (430 psi) for more than 500 milliseconds.
Action Taken When the DTC Sets
The DIM disables the A/C clutch.
Conditions for Clearing the DTC
| • | When the A/C refrigerant pressure drops to less than 1386 kPa (201 psi) 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 P1540 is stored as a history code it indicates that the DIM did receive a high A/C refrigerant pressure message from the PCM. This code could also be caused by an intermittent short to voltage on the sensor signal circuit, which would cause the PCM to set DTC P0530. The code could be the result of an actual A/C refrigerant high-pressure condition. |
| • | It is possible for the refrigerant system pressure to exceed 2968 kPa (430 psi) during extended engine idle speed with A/C on when ambient temperatures are greater than 41°C (105°F). This could be caused by: |
| - | An overcharged A/C system |
| - | A failed A/C pressure sensor |
| - | Blockage in a refrigerant line |
| - | Debris in front of the A/C condenser |
| - | Radiator or A/C condenser air shields missing or out of location |
| - | Inoperative engine cooling fans |
| - | Extended periods at idle in city traffic followed by rapid acceleration |
| - | Aftermarket products affecting cooling system performance |
| - | Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: HVAC Schematics Connector End View Reference: HVAC Connector End Views | ||||
1 | Did you perform the HVAC Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Is DTC P1540 stored as current? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
Does the scan tool indicate system pressure is within the pressure range shown on the pressure gage? | +20 to -20 psi | Go to Air Conditioning (A/C) System Performance Test in Heating, Ventilation and Air Conditioning. | Go to Step 4 |
4 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation and Air Conditioning. Did you complete the replacement? | -- | Go to Step 5 | -- |
5 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
