GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 Yukon - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 246-NP8 🢒 Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

Circuit Description

The transfer case shift control module controls the transfer case lock solenoid. The transfer case lock solenoid is released by being energized. This is accomplished by grounding the lock solenoid control circuit during gear shifts, and in the AUTO or adapt mode. Locking action is applied when power or ground are taken away from the lock solenoid, the transfer case motor is prevented from moving. The system is capable of providing a 2HI, 4HI and 4LO lock-up without the need of additional vehicle power to hold the transfer case in these positions.

The transfer case motor is a bi-directional, permanent magnet, D.C. motor. When energized, through motor control A or motor control B, the ground is provided by the opposing motor control circuit and then grounded through the transfer case shift control module ground circuit, the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the transfer case between the following ranges: 4HI, the AUTO or the Adapt mode (AWD), 2HI, Neutral (N) and 4LO.

If there is a fault in the brake control circuit, motor control A and B circuits are shorted together, or a motor control driver is damaged in the transfer case shift control module, the transfer case shift control module goes into a shift block mode. The transfer case module will also go into shift block mode if there is a mechanical concern causing the shift lever detent shaft to bind, or the transfer case shift control module is not seeing a signal from the park/neutral position (PNP) switch. The shift block mode causes the mode indicator to flash for a period of time when another mode is selected. After that period of time has ended, the indicator reverts back to the previous mode selection.

Test Description

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

  1. This step determines if the battery positive or ground circuits have an open or high resistance.

    2.

  2. This step helps to determine if the transfer case shift control module has the ability to command the encoder motor.

    3.

  3. This step determines if motor control A and motor control B circuits being shorted together is causing a shift block.

    4.

  4. This step determines if the motor control A and motor control B circuits are shorted together within the module.

    5.

  5. This step determines if a binding shift lever detent shaft is causing a shift block.

    6.

  6. This step has the transfer case removed and repaired.

    7.

  7. This step determines if the PNP switch is sending the correct range signal.

    8.

  8. This step replaces the transfer case shift control module.

    9.

  9. This step determines if a short to ground, short to voltage, open, or high resistance on the transfer case lock circuit is causing a shift block.

    10.

  10. This step replaced the encoder motor assembly.

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 - Transfer Case?

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

Test the battery positive voltage circuit and the ground circuit for an open or high resistance. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 3

3
  1. Turn the ignition ON, with the engine OFF.
  2. Install a scan tool.
  3. Go to ATC Data List on the scan tool and observe motor A and B current.
  4. Using the mode switch in the instrument panel, select the different modes.

Does the scan tool indicate an amperage draw from the motor?

Go to Step 4

Go to Step 8

4

Turn the ignition OFF and disconnect the transfer case shift control module, with a DMM, check to see if motor control A and motor control B are shorted together. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 5

5

Connect the transfer case shift control module, with a DMM, check motor control A and motor Control B circuits for being shorted together. Refer to Circuit Testing in Wiring Systems.

Did the DMM indicate the circuits are shorted together?

Go to Step 9

Go to Step 6

6

Remove the encoder motor and check to see if the shift lever detent shaft is binding. Refer to Transfer Case Encoder Motor Replacement .

Is the shift lever detent shaft binding?

Go to Step 7

Go to Step 10

7

Remove the transfer case and repair. Refer to Transfer Case Assembly Replacement .

Did you complete the repair?

Go to Step 12

--

8

Check the instrument panel to see if the correct transmission range is being displayed.

Is the correct range being displayed?

Go to Step 9

Go to Diagnostic System Check - Automatic Transmission In Automatic Transmission 4L60-E/4L65-E or Diagnostic System Check - Automatic Transmission In Automatic Transmission 4L80-E/4L85-E

9

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

Did you complete the repair?

Go to Step 12

--

10

Test the transfer case Lock circuit for a short to ground, short to voltage, open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

11

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

Did you complete the repair?

Go to Step 12

--

12
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for allowing the symptom to occur.

Does the symptom still occur?

Go to Step 2

System OK