GM Service Manual Online
For 1990-2009 cars only

Object Number: 377171  Size: MF
Transfer Case Control Components
Transfer Case Control Schematics

Circuit Description

The Transfer Case Shift Control Module controls the SERVICE indicator (AWD/4WD) lamp, located in the Instrument Cluster, by grounding circuit 1567. Voltage to the lamp is supplied via the Gauge Fuse, circuit 39. The fuse is located in the I/P Fuse Block.

Conditions for Setting the DTC

After the Transfer Case Shift Control Module commands the lamp on, the module senses a voltage greater than 7 V on circuit 1567.

Conditions for Clearing the DTC

    • The Transfer Case Shift Control Module will clear the DTC if the condition for setting the DTC no longer exists.
    • A history DTC will clear after 100 consecutive ignition cycles without a fault present.
    • Use a scan tool in order to clear history DTCs.

Test Description

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

  1. This step determines whether circuit 1567 is shorted to voltage.

  2. Jumping terminal E2 of the transfer case shift control module harness connector to ground should provide a complete path to ground for the Service 4WD lamp. This step attempts to eliminate the instrument cluster and wiring from fault.

DTC B0768 Service Indicator Circuit High

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. Turn the ignition OFF.
  2. Disconnect the instrument cluster connector.
  3. Inspect the instrument cluster connector terminals for damage or corrosion

Are the terminals damaged or corroded?

--

Go to Step 5

Go to Step 3

3

  1. Disconnect the instrument cluster harness connector.
  2. Disconnect both transfer case shift control module connectors.
  3. Connect the J 39200 Digital Multimeter (DMM) between connector  C1 terminal E2 at the transfer case shift control module harness and ground.
  4. Turn the ignition to RUN.

Is the voltage reading greater than the specified voltage?

0 V

Go to Step 4

Go to Step 6

4

Repair a short to voltage in CKT 1567. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 11

--

5

Repair the instrument cluster wire harness connector. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete?

--

Go to Step 11

--

6

  1. Turn the ignition OFF.
  2. Reconnect the instrument cluster.
  3. Connect a 3 A fused jumper wire from terminal E2 at the transfer case shift control module to ground.
  4. Turn the ignition to RUN.

Does the Service 4WD lamp light?

--

Go to Step 7

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 11

--

8

Inspect instrument cluster Service 4WD lamp for faulty bulb.

Is the bulb good?

--

Go to Step 10

Go to Step 9

9

Replace instrument cluster SERVICE 4WD bulb. Refer to Instrument Cluster Bulb Replacement .

Is the repair complete?

--

Go to Step 11

--

10

Remove instrument cluster for service. Refer to Instrument Cluster Replacement .

Is the repair complete?

--

Go to Step 11

--

11

  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 12

--

12

Clear all ATC DTCs.

Have all the ATC DTCs been cleared?

--

Go to Transfer Case Diagnostic System Check

--