P1540

CIRCUIT DESCRIPTION
The powertrain control module (PCM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The PCM applies a 5 volt reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the A/C refrigerant pressure input to the PCM to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When the pressure is high the PCM commands the cooling fans on. When the pressure is too high or 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 and set DTC P1540 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 compressor 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 compressor clutch.
^ The history DTC will clear after 40 fault free 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 also 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:
- 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 problem is intermittent, refer to Testing for Intermittent and Poor Connections in Diagnostic Aids.

TEST

Steps 1-5: