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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P1546

DTC P1546 3.8L

Circuit Description

Ignition voltage is supplied directly to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit via 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 9.0-18.0 volts.
    • The engine speed is more than 80 RPM.
    • The PCM driver is activated.

Conditions for Setting the DTC
    • The PCM detects an improper voltage level on the output circuit that controls the A/C relay.
    • The condition is present for at least 30 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 fault-free ignition cycles.
    • The DTC can be cleared with a 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 voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power 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 battery positive 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 battery positive 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 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 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 battery positive 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.

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

DTC P1546 5.7L

Circuit Description

The PCM will activate the A/C clutch relay when the PCM detects that A/C has been requested. When the PCM activates the relay, voltage should be present at both the A/C compressor clutch and the A/C compressor clutch supply voltage circuit at the PCM. If voltage is not detected when A/C is requested this DTC sets.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC
    • The PCM detects that A/C has been requested.
    • The PCM commands the A/C compressor clutch driver ON.
    • The PCM does not detect a voltage on the A/C compressor clutch supply voltage circuit that supplies voltage to the A/C compressor clutch.
    • The condition is present for at least 20 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 fault-free ignition cycles.
    • The DTC can be cleared with a scan tool.

Test Description

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

  1. Verifies that battery voltage is supplied to the A/C compressor clutch relay.

    2.

  2. Tests if the A/C relay is at fault or the A/C compressor clutch supply voltage circuit is at fault.

    3.

  3. If the A/C clutch feedback signal parameter displays OFF, this indicates the PCM does not recognize voltage from the A/C compressor clutch supply voltage circuit.

    4.

  4. Tests for a high resistance or an open.

    5.

  5. 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 on the A/C and let the engine idle for 5 minutes.
  4. With a scan tool, observe the A/C clutch feedback signal parameter in the Powertrain, Engine Data 2 list.

Does the A/C Clutch Feedback Signal Display, Relay ON?

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

Go to Step 3

3

Important: For underhood electrical center relay terminal identification refer to Electrical Center Identification Views in Wiring Systems.

  1. Turn OFF the ignition.
  2. Remove the A/C compressor clutch relay from the electrical center 2.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit at the A/C compressor clutch relay terminal with the test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 9

4

Install a 10-amp fused jumper wire between the ignition 1 voltage circuit and the A/C compressor clutch supply voltage circuit.

Does the A/C compressor clutch engage?

Go to Step 5

Go to Step 10

5

Important: The fused jumper wire should still be installed with the ignition ON.

With a scan tool, observe the A/C Clutch Feedback Signal parameter.

Does the A/C Clutch Feedback Signal Display, Relay ON?

Go to Step 7

Go to Step 6

6

Test the A/C compressor clutch supply voltage circuit for a high resistance or an open between S105 and the PCM. Refer to Circuit Testing in Wiring Systems.

Is the action complete?

Go to Step 13

Go to Step 8

7

Inspect for poor connections at the A/C compressor 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

8

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

9

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

--

10

Repair the A/C compressor clutch supply voltage circuit from the A/C compressor clutch relay to the circuit splice. 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 reprogramming procedure for the powertrain control module .

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

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