GM Service Manual Online
For 1990-2009 cars only

Object Number: 380647  Size: MF
Transfer Case Control Components
Transfer Case Control Schematics

Circuit Description

The indicator lamps circuit consist of five individual lamps contained inside the mode/range switch assembly. They are AUTO, 4WD, 2HI, 4HI, 4LO and Neutral. The AUTO, 4WD, 2HI, 4HI, and 4LO lamps are contain inside their respective range button. When the ignition in ON, the automatic transfer case control module illuminates the indicator lamp that corresponds to the current ATC gear position by providing a ground through a current limiting driver.

The automatic transfer case control module flashes each indicator lamp after a shift has been requested and will continue to flash until the automatic transfer case control module can complete the shift. After a shift to AUTO, 4WD, 4HI, or 4LO is made, the automatic transfer case control module will flash that indicator lamp until the automatic transfer case control module receives a high voltage signal on circuit 1695 from the front axle switch.

A solid state circuit located inside the switch supplies ignition voltage to the lamps. The solid state circuit also receives voltage whenever the headlamp switch is in park or headlamp position. When the solid state circuit receives voltage from the headlamp switch it will reduce the voltage that it supplies to the indicator lamps, dimming the lamps when the headlamps are ON.

Test Description

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

  1. This step determines if the transfer case shift control module has electronic control of the switch indicator lamps.

  2. This step provides a ground to the indicator lamp circuits in order to eliminate the transfer case shift control module.

  3. This step checks for B+ in the indicator lamp circuits.

One or More Switch Indicator Lamps Does Not Light

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 ignition to RUN, engine OFF.
  3. Use the Scan Tool in order to command each of the switch indicator lamps On.

Do the switch indicator lamps turn On?

--

Go to Step 7

Go to Step 3

3

  1. Use the Scan Tool to view the ATC Data List.
  2. Observe the states of the Indicator Lamps.
  3. Use the Scan Tool in order to command each of the switch indicator lamps On.

Do each of the switch indicator lamp states change from OFF to ON as Indicator Lamps are commanded ON?

--

Go to Step 7

Go to Step 4

4

  1. Disconnect both connectors at the transfer case shift control module.
  2. Use a fused jumper wire in order to jump to ground each of the indicator lamp circuits.

Do each of the lamps illuminate when its circuit is grounded?

--

Go to Step 7

Go to Step 5

5

Connect a J 39200 Digital Multimeter DMM between the suspect circuit and ground in order to measure voltage.

Is the voltage within the specified value?

9-14 V

Go to Step 8

Go to Step 6

6

Inspect the suspect circuit(s) for open. Refer to Wiring Repairs in Wiring Systems.

Were the suspected circuit(s) open?

--

Go to Step 9

Go to Step 8

7

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

Is the action complete?

--

Go to Step 10

--

8

Replace the range/mode switch. Refer to Transfer Case Shift Control Switch Replacement .

Is the action complete?

--

Go to Step 10

--

9

Repair an open in the suspect circuit(s). Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 10

--

10

  1. Ensure the ignition is OFF.
  2. Properly mount and reconnect all previously disconnected ATC components.

Have all the ATC components been reconnected and properly mounted?

--

Go to Step 11

--

11

Clear all ATC DTCs.

Have all the ATC DTCs been cleared?

--

Go to Transfer Case Diagnostic System Check

--