P1540 - FAULT CODE - OBD2

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.

• Check Engine lamp comes on.
• The air conditioning clutch remains disengaged.

The reasons why the P1540 OBDII fault code is set are:

• The amount of air conditioning refrigerant may be low.
• The A/C System Pressure Sensor circuit may have damage to its wires or connectors.
• The refrigerant lines may be clogged.
• The engine cooling fans may not be working properly.
• The A/C system pressure sensor could be faulty.

The corresponding steps to troubleshoot the DTC P1540 OBD2 code are:

• Consult the Technical Service Bulletins.
• Using a scan tool it is necessary to check if other fault codes related to the air conditioning system are configured. Repair these codes if present.
• Verify that the amount of A/C refrigerant available is adequate for proper operation of the A/C system. If you discover an excessively low level, you should make the appropriate adjustments.
• Check the air conditioner refrigerant lines for obstructions that would prevent the passage of refrigerant. Correct it as applicable.
• Inspect the A/C system pressure sensor wiring and measure its circuit voltages. If you discover damage to the wiring or out-of-range voltages, make repairs.