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For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H2 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

Circuit Description

The transfer case shift control module flashes each indicator lamp after a shift has been requested and continues to flash until the transfer case shift control module can complete the shift. If the transfer case is unable to make a shift, the requested mode indicator flashes and returns to the previous mode. If the requested mode indicator flashes for 15 seconds and returns to the previous mode, this indicates the loss of a necessary input from another module. The transfer case shift control module requires a vehicle speed sensor (VSS) signal, provided by the antilock brake system (ABS) module, and a PRNDL input provided by the transmission. These signals are provided to the transfer case shift control module via class 2, and if not received the transfer case will not shift.

If a new mode is requested and the requested mode indicator flashes less then 15 seconds and returns to the previous mode, this indicates a transfer case fault. This symptom is caused by an internal mechanical transfer case fault causing the shift detent lever shaft to bind, or a fault within the encoder motor.

Test Description

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

  1. This step tests for the possibility of a missing system input or a system fault.

    2.

  2. This step tests for a missing PRNDL input from the transmission.

    3.

  3. This step tests for a missing VSS signal from the ABS system.

    4.

  4. This step determines if the condition is caused by a faulty encoder motor or a mechanical internal fault to the transfer case.

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Component Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Turn ON the ignition, with the engine OFF.
  2. Place the vehicle in Neutral.
  3. Select a different mode on the transfer case shift control switch.

Does the switch flash the full 15 seconds?

Go to Step 3

Go to Step 5

3

  1. Connect a scan tool to the vehicle.
  2. Test for transmission DTCs indicating loss of the PRNDL signal.

Is a DTC set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Step 4

4

With the scan tool, test for ABS DTCs indicating a loss of VSS.

Is a DTC set?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

Go to Testing for Intermittent Conditions and Poor Connections

5

  1. Remove the transfer case encoder motor, while leaving the electrical harness connected.
  2. Attempt to shift the transfer case to a different mode.

Is the encoder motor able to make the shift?

Go to Step 7

Go to Step 6

6

Replace the transfer case encoder motor. Refer to Transfer Case Motor/Encoder Replacement .

Is the repair complete?

Go to Step 8

--

7

Remove the transfer case and repair, for a shift detent lever shaft binding condition. Refer to Transfer Case Disassemble .

Is the repair complete?

Go to Step 8

--

8
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle in order to determine if the symptom has been corrected.

Is the symptom still present?

--

System OK