GM Service Manual Online
For 1990-2009 cars only

Refer to Engine Controls Schematics

Heater A/C Control and A/C Compressor Clutch Coil


Object Number: 588176  Size: FS
DIC/HVAC and HVAC CTRL Fuse
DIC/HVAC and HVAC CTRL Fuse
Handling ESD Sensitive Parts Notice
Underhood Accessory Wiring Junction Block, ICM, Automatic Transaxle, Stop Lamp Switch and EBCM
Handling ESD Sensitive Parts Notice
G117
G117
Engine Controls Components
Powertrain Control Module Description
Coolant Fan Motor #1 and Coolant Fan Motor #2
Automatic Transaxle, EBCM, Performance Shift Switch and Stop Lamp Switch
OBD II Symbol Description Notice
.

Circuit Description

The powertrain control module (PCM) uses the output driver modules (ODMs) in order to turn on many of the current-driven devices that are needed to control various engine and transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding ON. Unlike the quad driver modules (QDMs) used in prior model years, ODMs are capable of individually diagnosing each output circuit. If an improper voltage level is detected on the output circuit that controls the A/C compressor control relay, DTC P1546 will set.

Conditions for Setting the DTC

    • The ignition is ON.
    • An improper voltage level has been detected on the output circuit that controls the A/C compressor control relay.
    • The above conditions are present for at least 30 seconds.

Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC

    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction free warm-up cycles.
    • The PCM receives a clear code command from the scan tool.

Diagnostic Aids

Inspect for the following conditions:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

    • Loose terminal connection
       -  Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
       -  Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
    • Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.
    •  Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Test Description

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

  1. The Powertrain On Board (OBD) System Check prompts you to complete some basic tests and to store the freeze frame and failure records data on the scan tool.

  2. Listen for a click when the relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

  3. This step tests for voltage at the coil feed side of the relay.

  4. This step verifies that the PCM is providing ground to the relay.

  5. This step tests if ground is constantly being applied to the relay.

  6. The PCM utilizes an electrically erasable programmable read-only memory (EEPROM). When you replace the PCM, you must program the new PCM.

DTC P1546 A/C Relay Circuit Fault

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn ON the ignition, with the engine OFF.
  2. Use a scan tool in order to command the A/C relay ON and OFF.

Does the relay turn ON and OFF with each command?

--

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the coil feed circuit of the relay using a test lamp connected to 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 relay and the coil feed circuit of the relay.
  2. Use a scan tool in order to 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

  1. Test the control circuit of the relay for a short to voltage or for an open.
  2. If you find a problem, repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

7

  1. Test the control circuit of the relay for a short to ground.
  2. If you find a problem, repair the condition as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

8

Inspect for faulty connections at the 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 faulty connections at the PCM. 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

Important: If the fuse is open, locate and repair a short to ground in either the relay feed circuit, the A/C clutch feed circuit, or an internal short to ground in the relay.

Repair the feed circuit of the relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 13

--

11

Replace the relay. Refer to Compressor Relay Replacement in HVAC System-Manual.

Did you complete the replacement?

--

Go to Step 13

--

12

Important: Perform the set up procedure for the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Did you complete the replacement?

--

Go to Step 13

--

13

  1. Use the scan tool in order to record the Failure Records and to clear the DTCs .
  2. Operate the vehicle within the Failure Record conditions.

Does the DTC reset?

--

Go to Step 2

System OK