GM Service Manual Online
For 1990-2009 cars only

Test Description

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

  1. Helps determine whether the front axle switch is functioning properly.

  2. Helps determine whether the front axle switch is locking and unlocking.

  3. Tests transfer case clutch performance.

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics

1

Did you perform the Transfer Case Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Turn the ignition ON, with the engine OFF.
  2. Ensure that the vehicle is in 4WD mode.
  3. Install a scan tool.
  4. Use the scan tool in order to read the Front Axle Switch status.

Does the scan tool display the Front Axle Switch status as Locked?

Go to Step 3

Go to Front Axle Will Not Engage

3

  1. Change the vehicle's transfer case mode from 4WD to AWD mode.
  2. Use the scan tool in order to read the Front Axle Switch status.

Does the scan tool display the Front Axle Switch status as Locked?

Go to Step 4

Go to Step 6

4

  1. Change the vehicle's transfer case mode back from AWD to 4WD mode.
  2. Drive the vehicle for a short test drive while observing the ATC Data List.
  3. Note the values of the Front and Rear Propshaft Speed at a set speed.
  4. Compare the Front and Rear Propshaft speed previously noted at the same speeds.

Are the RPM values approximately equal at the same speeds?

Go to Step 6

Go to Step 5

5

  1. Inspect the front axle and transfer case for a mechanical malfunction.
  2. Repair/Replace as needed.

Is the repair complete?

Go to Step 7

--

6

Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .

Is the repair complete?

Go to Step 7

--

7

  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for allowing the symptom to re-occur.

Does the symptom re-occur?

Go to Step 2

System OK