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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Transfer Case Shift Control Switch Indicators Flash Continuously 15 Seconds or More

Circuit Description

This symptom is usually the result of actions expected to take place during the transition of a transfer case mode change, which has not happened. When the transfer case changes from 2WD to 4WD, for example, the front axle is Locked by the transfer case shift control module. If the transfer case shift control module does not sense that the front axle is applied, the module waits for the action to take place before the gear change is made. While waiting, the mode switch lamp continues to flash for a period of time, at which time all other mode requests are ignored for the duration of the ignition cycle.

The front axle control circuit consists of an electric motor actuator which engages and disengages the front axle. The front axle actuator motor consists of the following components contained within the actuator assembly:

    • A permanent magnetic motor
    • A worm gear controlled plunger
    • A front axle switch
    • An electronic control circuit

The front axle actuator consists of the following circuits:

    • The front axle control circuit, which is also connected to the transfer case shift control module
    • The front axle switch circuit, which is also connected to the transfer case shift control module
    • A battery feed circuit
    • A ground circuit

When a shift to AUTO 4WD, 4HI, or 4LO is requested, the transfer case shift control module engages the front axle by grounding the front axle control circuit through a current limiting driver.

Test Description

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

  1. This step determines the position of the front axle switch.

    2.

  2. This step helps determine if the front axle will not engage.

    3.

  3. This step helps determine if the front axle will not disengage.

Step

Action

Yes

No

Schematic Reference: Transfer Case Control Schematics

Connector End View Reference: Transfer Case Control 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 the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Using a scan tool, observe the Front Axle Switch parameter.

Does the scan tool display the Front Axle Switch status as Locked?

Go to Step 4

Go to Step 3

3

Using a scan tool, observe the Encoder Gear Position parameter.

Is the transfer case in 4WD HI or 4WD Low mode?

Go to Front Axle Will Not Engage

Go to Step 5

4

Using a scan tool, observe the Encoder Gear Position parameter.

Is the transfer case in 2WD mode?

Go to Front Axle Will Not Disengage

Go to Step 5

5

Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming.

Did you complete the repair?

Go to Step 6

--

6
  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?

Go to Step 2

System OK