Circuit Description
The A/C system uses an A/C refrigerant pressure sensor mounted in the high pressure side of the A/C refrigerant system to monitor A/C refrigerant pressure. The powertrain control module (PCM) uses this information to turn ON the engine coolant fans when the A/C refrigerant pressure is high and to keep the compressor disengaged when A/C refrigerant pressure is excessively high or low. The A/C refrigerant pressure sensor operates like other 3 wire sensors. The PCM applies a 5 volt reference and a sensor ground to the sensor. Changes in the A/C refrigerant pressure will cause the A/C refrigerant pressure input to the PCM to vary. The PCM monitors the A/C refrigerant pressure sensor signal circuit. 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 and set DTC P1540.
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 A/C refrigerant pressure sensor signal circuit which would cause the PCM to set DTC P0530. The code could be the result of an actual A/C refrigerant over-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 the following conditions: |
| - | An overcharged A/C system |
| - | A failed A/C refrigerant 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 |
| • | If the concern is intermittent, 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 near the gauge pressure within the specified range? | -138 to +138 kPa (-20 to +20 psi) | 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 |
