GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The indicator lamps circuit consists of three individual lamps contained inside their respective buttons making up the transfer case select switch assembly. They are the 2HI, 4HI and 4LO lamps. When the ignition switch is placed in the RUN position, current is provided to the switch assembly. The transfer case shift control module provides a ground for the lamps when a particular gear is active or when the transfer case is in transition. Through solid state circuity located inside the switch assembly, voltage can be regulated to provide less illumination when the headlamps or parking lights are turned ON.

Test Description

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

  1. This step helps to determine intermittent conditions.

  2. This step helps to determine if the transfer case shift control module is commanding more than one lamp ON.

  3. This step tests and repairs a short to ground in the indicator control circuits.

  4. This step tests if more than one indicator control circuits are shorted together.

Switch Indicator Lamps Remain ON -- Two or More

Step

Action

Value(s)

Yes

No

1

Did you perform A Diagnostic System Check - Transfer Case?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Cycle the ignition switch from ON to OFF and wait ten seconds.
  2. Start the vehicle and drive.

Do two or more switch indicator lamps still remain ON?

--

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

  1. Turn OFF the ignition.
  2. Disconnect the connectors at transfer case shift control module.
  3. Turn ON the ignition, with the engine OFF.

Do all the switch indicator lamps stay OFF?

--

Go to Step 5

Go to Step 4

4

Repair a short to ground on the suspect indicator control circuit(s) (the one(s) that remain ON). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 8

Go to Step 6

5

Test the suspect indicator control circuit(s) to determine if they are shorted together. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 8

Go to Step 7

6

Replace the shift control switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the replacement?

--

Go to Step 8

--

7

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

Did you complete the replacement?

--

Go to Step 8

--

8

Operate the vehicle within the conditions for causing the symptom as specified in the supporting text.

Does the symptom re-occur?

--

Go to Step 2

System OK