GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon XL - 2WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 263-NP1 (Selectable) 🢒 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, it waits for the action to take place before the gear change is made. While waiting, the shift control switch indicator will continue to flash for a period of time, at which time all other mode requests will be 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 consists of a Permanent Magnetic (PM) motor, a worm gear controlled plunger, a front axle switch and an electronic control circuit all within the actuator assembly.

The front axle actuator has four circuits connected:

    • Ignition 3 voltage circuit
    • Ground circuit
    • Axle actuator control circuit
    • Axle switch signal circuit

Whenever a shift to 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 actuator.

    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

1

Was the Transfer Case Diagnostic System Check performed?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Turn ON the ignition, with the engine OFF.
  2. Install a scan tool.
  3. Use the scan tool in order to read the Front Axle Switch Status.

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

Go to Step 4

Go to Step 3

3

Use the scan tool in order to read the Encoder Gear Position status.

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

Go to Front Axle Will Not Engage

Go to Step 5

4

Use the scan tool in order to read the Encoder Gear Position status.

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 the Transfer Case Shift Control Module Replacement .

Did you complete the replacement?

Go to Step 6

--

6
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the conditions for allowing the symptom to re-occur.

Does the symptom re-occur?

Go to Step 2

System OK