GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2002 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0645

Circuit Description

Ignition 1 voltage is supplied directly to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

Conditions for Running the DTC
    • The ignition voltage is between 6.0-18.0 volts.
    • The engine speed is greater than 400 RPM.

Conditions for Setting the DTC
    • Commanded state does not equal actual state of the control circuit.
    • The condition is present for at least 5 seconds.

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. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Tests for ignition 1 voltage at the coil side of the A/C compressor clutch relay. The 15 Amp fuse supplies ignition 1 voltage to the coil side of the A/C compressor clutch relay.

    3.

  3. Verifies that the powertrain control module is providing ground to the A/C compressor clutch relay.

    4.

  4. Tests if ground is constantly being applied to the A/C compressor clutch relay.

    5.

  5. Tests for a short to voltage or an open.

    6.

  6. 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

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the A/C Relay ON and OFF in the Special Functions, Engine Output Controls list.

Does the A/C Relay turn ON and OFF with each command?

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

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the A/C compressor clutch relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit of the A/C compressor clutch relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the control circuit of the A/C compressor clutch relay and the ignition 1 voltage circuit of the A/C compressor clutch relay.
  2. With a scan tool, command the A/C Relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the A/C compressor clutch relay control circuit of the A/C compressor clutch relay for a short to voltage or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the A/C compressor clutch relay control circuit of the A/C compressor clutch relay for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the A/C compressor clutch relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the powertrain control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the ignition 1 voltage circuit of the A/C compressor clutch relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the A/C compressor clutch relay.

Did you complete the replacement?

Go to Step 13

--

12

Important: Perform the recalibration 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 13

--

13
  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