GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Did you perform the Transfer Case Diagnostic System Test?

--

Go to Step 2

Go to Diagnostic System Check in Transfer Case

2

Inspect the 4WD indicator lamp. Refer to Switch Indicator Lamps Remain ON - Two or More in Transfer Case.

Does the 4WD indicator lamp turn off?

--

System OK

Go to Step 3

3

Check the electrical system of the front drive axle. Refer to Front Axle Will Not Disengage in Transfer Case.

Does the 4WD disengage?

--

System OK

Go to Step  4

4

Inspect the vacuum hoses.

Are the vacuum hoses kinked, disconnected, damaged or plugged?

--

Go to Step  5

Go to Step 6

5

Replace the vacuum hoses.

Does the 4WD disengage?

--

System OK

Go to Step 6

6

Inspect for engine vacuum at the vacuum actuator.

Is there vacuum at the actuator?

--

Go to Step 8

Go to Step 7

7

Replace the vacuum actuator. Refer to Vacuum Actuator Replacement .

Does the 4WD disengage?

--

System OK

Go to Step 8

8

Inspect the cable.

Is the cable damaged, disconnected or binding?

--

Go to Step 9

Go to Step 10

9

Replace the cable. Refer to Shift Cable Replacement .

Does the 4WD disengage?

--

System OK

Go to Step 10

10

inspect the operation of the shift fork. Use J 33798 . Refer to J 33798 - Hub Engagement Tool .

Does the 4WD disengage?

--

System OK

Go to Step 11

11

Replace the shift fork. Refer to Shift Fork Replacement .

Does the 4WD disengage?

--

System OK

Go to Step 12

12

The cause of concern may be in the front drive axle. Disassemble the front drive axle. Inspect for damaged components. Refer to Differential Carrier Assembly Disassemble .

Does the 4WD disengage?

--

System OK

Go to Step 1