GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2002 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P1539

Circuit Description

The PCM will activate the A/C clutch relay when the PCM detects an A/C requested. Voltage is present at both A/C compressor clutch and the A/C clutch status terminal at the PCM when the relay is activated. A DTC P1539 sets if the PCM detects a voltage on the A/C compressor clutch supply voltage circuit when the system had not requested the A/C. A short to voltage on the A/C compressor clutch supply voltage circuit, or the A/C relay contacts are stuck, sets a DTC P1539.

Conditions for Running the DTC

The A/C is OFF.

Conditions for Setting the DTC

The PCM detects a voltage on the A/C compressor clutch supply voltage circuit when the A/C is not requested.

Action Taken When the DTC Sets
    • The PCM will not illuminate the Malfunction Indicator Lamp (MIL).
    • The PCM stores the failure records.
    • The A/C compressor clutch is disabled.

Conditions for Clearing the DTC
    • The DTC will become history if the PCM no longer detects a failure.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • A last test failed DTC will clear when the diagnostic runs and does not fail.
    • The DTC can be cleared by using the scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Verifies the condition is present.

    2.

  2. Determines if the A/C compressor clutch relay is at fault.

    3.

  3. Determines if the PCM is at fault or the A/C compressor clutch supply voltage circuit is at fault.

    4.

  4. Perform the recalibration procedure for the powertrain control module.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Manual

2

Important: Diagnose P0645 first if it is set.

  1. Install a scan tool.
  2. Start the engine.
  3. Turn OFF the A/C and let the engine idle.
  4. With a scan tool, observe the A/C Request Signal and the A/C Relay Command parameters in the Powertrain, Engine Data 2 list.

Does the A/C Request Signal display YES and the A/C Relay Command display Relay ON when the A/C is not requested?

Go to HVAC Compressor Clutch Does Not Engage or HVAC Compressor Clutch Does Not Disengage

Go to Step 3

3

With a scan tool, observe the A/C Clutch Feedback Signal in the Powertrain, Engine Data 2 list.

Does the A/C Clutch Feedback Signal display Engaged?

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

4

Remove the A/C compressor clutch relay.

Does the A/C Clutch Feedback Signal display Disengaged?

Go to Step 6

Go to Step 5

5

Test the A/C compressor clutch supply voltage circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

6

Replace the A/C compressor clutch relay.

Did you complete the replacement?

Go to Step 8

--

7

Important: Perform the reprogramming procedure for the powertrain control module .

Replace the powertrain control module. Refer to Powertrain Control Module Replacement in Engine Controls-5.7L.

Did you complete the replacement?

Go to Step 8

--

8
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK