GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2006 🢒 Terraza - 4WD 🢒 Driveline/Axle 🢒 Drive Axle - Locking/Limited Slip 🢒 All-Wheel Drive Disabled Indicator Always On

Circuit Description

The differential clutch pump actuator check valve assembly is a pulse width modulated actuator mounted to the rear drive assembly. Ignition voltage is supplied to the clutch pump actuator check valve through a fused circuit. The powertrain control module (PCM) or the transmission control module (TCM) controls the actuator with a negative duty cycle. The actuator controls the supply fluid to the pump inlet in the rear drive assembly. When the actuator is commanded OFF, the PCM/TCM will detect a high voltage. When the actuator is commanded ON, the PCM/TCM will detect a low voltage. At engine start-up, the actuator is turned ON at 49-90 percent duty cycle for 3 seconds, then drops to 16-28 percent for holding. Every 30 seconds, the duty cycle is ramped to 49-90 percent for 0.5 second, then back to 16-28 percent. If the PCM/TCM detects a voltage on the axle actuator circuit that is outside of the calibrated limits then the all-wheel drive (AWD) disable lamp illuminates.

Conditions for Running the All-Wheel Drive (AWD) Disable Fault
    • The system voltage is 9-18 volts.
    • The engine speed is greater than 500 RPM for 5 seconds, and the engine is not in fuel shut-off.
    • The rear drive module must not be in an overtemperature condition.

Conditions for Turning On the All-Wheel Drive (AWD) Disable Lamp

The AWD disable lamp illuminates when one of the following conditions exists for 5 seconds:

    • The PCM/TCM commands the solenoid ON and the voltage feedback remains high, B+.
    • The PCM/TCM commands the solenoid OFF and the voltage feedback remains low, 0 volts. This condition is present for 3 key cycles.

Action Taken When the All-Wheel Drive (AWD) Lamp Illuminates
    • The PCM/TCM does not illuminate the malfunction indicator lamp (MIL).
    • The PCM/TCM inhibits AWD.

Conditions for Clearing the All-Wheel Drive (AWD) Disable Fault

The PCM/TCM cancels the fault default actions when the fault no longer exists.

Important: When an AWD mini spare disable condition is present, after correcting the condition, the vehicle must be driven 0.5 km (0.3 mi) in a straight line and then brought to a complete stop before the PCM/TCM will command the AWD disable lamp OFF.

Test Description

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

  1. This step tests the ignition 1 voltage circuit for proper voltage.

    2.

  2. This step tests the ground circuit for an open.

    3.

  3. This step tests the axle actuator control circuit duty cycle.

    4.

  4. This step tests the axle actuator control circuit for an open or short.

Step

Action

Value(s)

Yes

No

Schematic Reference: All-Wheel Drive Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Verify the fault is present.

Does the system operate normally?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Disconnect the differential clutch pump actuator check valve.
  2. Turn ON the ignition, with the engine OFF.
  3. Using a DMM, test the ignition 1 voltage circuit for proper voltage.

Does the voltage measure within the specified value?

9-14 V

Go to Step 4

Go to Step 7

4

  1. Connect a test lamp between the ignition 1 voltage circuit and the ground circuit at the differential clutch pump actuator check valve.
  2. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 8

5

  1. Turn the ignition OFF.
  2. With the connector connected, connect a DMM in parallel to the control circuit. Set the DMM to read duty cycle.

    3. Important: The differential clutch pump actuator check valve duty cycle will initiate at 49-90 percent duty cycle for 3 seconds, then drop to 16-28 percent duty cycle. Every 30 seconds, the duty cycle will cycle up to 49-90 percent for 0.5 seconds, then back to 16-28 percent.

  3. Start the engine.
  4. Observe AWD Duty Cycle on the DMM from the time of engine start.

Is the duty cycle functioning as described?

HI Range: 49-90%

LO Range: 16-28%

Go to Step 9

Go to Step 6

6

Test the axle actuator control circuit for the following conditions:

    • An open
    • A short to voltage
    •  A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

7

Locate and repair an open or short to ground in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

--

Go to Step 11

--

8

Locate and repair an open in the ground circuit. Refer to Testing for Continuity and Wiring Repairs .

Did you complete the repair?

--

Go to Step 11

--

9

Replace the differential clutch pump actuator check valve. Refer to Differential Clutch Pump Check Valve Replacement .

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the PCM for 3.5L or the TCM for 3.9L. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 11

--

11
  1. Use the scan tool in order to clear the faults.
  2. Operate the vehicle within the Conditions for Running the All-Wheel Drive (AWD) Disable Fault, as specified in the supporting text.

Does the fault set?

--

Go to Step 3

Go to All-Wheel Drive (AWD) System Functional Inspection