GM Service Manual Online
For 1990-2009 cars only

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. The front axle switch should be in the Locked position while the vehicle is in the 4WD mode. This step determines if the front axle switch is Locked during 4WD mode.

  2. This step determines if the front axle switch is Locked during AWD mode.

  3. This step determines if there is a mechanical failure or a faulty transfer case shift control module.

No Correction For Slip In AWD Mode

Step

Action

Value(s)

Yes

No

1

Was the Transfer Case Diagnostic System Check performed?

--

Go to Step 2

Go to Transfer Case Diagnostic System Check

2

  1. Connect a Scan Tool .
  2. Turn the engine ON.
  3. Ensure the vehicle is in 4WD mode.
  4. Use the Scan Tool in order to view the state of the Front Axle Switch.

Is the Front Axle Switch Locked?

Go to Step 3

Go to Front Axle Will Not Engage

3

  1. Change Range/Mode state to AWD.
  2. Use the Scan Tool in order to view the state of the Front Axle Switch.

Does the state of the Front Axle Switch continue to display Locked?

--

Go to Step 4

Go to Step 6

4

  1. Change Range/Mode state to back 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 speed.

Are the rpm values approximately equal at the same speeds?

--

Go to Step 6

Go to Step 5

5

Inspect front axle and transfer case for mechanical failure. Repair/replace as needed.

Are the repairs complete?

--

Go to Step 7

--

6

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

Is the action complete?

--

Go to Step 7

--

7

Reconnect all ATC system components, make sure all the components are properly mounted.

Have all the ATC components been reconnected and properly mounted?

--

Go to Step 8

--

8

Clear all the ATC DTCs.

Are all the ATC DTCs cleared?

--

Go to Transfer Case Diagnostic System Check

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