P1540 BUICK, CADILLAC, CHEVROLET, GMC: A/C SYSTEM HIGH PRESSURE
POST UPDATED IN May, 2023
P1540 BUICK, CADILLAC, CHEVROLET, GMC: A/C SYSTEM HIGH PRESSURE
The Powertrain Control Module (PCM) continuously checks the air conditioning high side refrigerant pressure through the use of the A/C Refrigerant Pressure Sensor. If the pressure is low, the signal voltage will be low, and when the pressure is high, the PCM, taking into account this condition, orders the activation of the cooling fans. In case the pressure is excessively out of normal parameters, the PCM does not allow the A/C compressor clutch to engage.
The Powertrain Control Module provides the A/C pressure data to the DIM (Dash Integration Module) via the class 2 serial data circuit. The DIM will accordingly command the in-line A/C orifice solenoid to decrease or increase the high side pressure as needed. This action keeps the high side pressure within the normal operating range, and also prevents the compressor clutch from disengaging under normal operating conditions, noting that the DIM does not request engagement of the compressor clutch if the system pressure is too high.
The PCM sets diagnostic code P1540 OBD2 when it detects that the A/C System Pressure Sensor does not meet the manufacturer’s specifications. This condition is caused by the A/C refrigerant pressure being higher than 2968 kPa for a certain amount of time.
The reasons why the P1540 OBDII fault code is set are:
The corresponding steps to troubleshoot the DTC P1540 OBD2 code are: