GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Sonoma Pickup - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 236/246-NP8 (Two Speed Automatic) 🢒 Transfer Case Shift Control Switch Indicator Flashes, then Returns to Previous Mode

Circuit Description

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 4H, AUTO 4WD, 2H, N, and 4L ranges. While the transfer case motor is energized the transfer case shift control module also energizes the solenoid for the transfer case lock. The motor lock is disabled (locking action released) and free turning of the transfer case motor and sector shaft is then allowed.

This symptom indicates a short to ground, short to power, or high resistance in the Motor Control A, Motor Control B, or Lock Solenoid Control circuits

Test Description

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

  1. This step determines if any DTCs have set.

    2.

  2. Tests for an open or high resistance in the motor windings.

    3.

  3. Tests for an open or high resistance in the lock solenoid windings.

    4.

  4. This step determines if the module is sending voltage through the motor control A circuit.

    5.

  5. This step determines if the module is sending voltage through the motor control B circuit.

    6.

  6. This step determines if the reason voltage is not get from the transfer case shift control module to the encoder motor through motor control A and B circuits is due to an open or high resistance in these circuits.

    7.

  7. This step determines if the proper 8 V reference signal is coming from the transfer case shift control module.

    8.

  8. This step determines if the module is producing the correct voltage through the P, A, B, and C channels.

    9.

  9. Tests the encoder signal ground circuit for an open or high resistance.

Step

Action

Value(s)

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

Were any DTC's indentified in the diagnostic system check?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Turn the ignition OFF
  2. Disconnect the four wire connector at the transfer case.
  3. With a DMM measure the resistance of the encoder motor, and jumper harness by probing motor control A and motor control B circuits.

Is the resistance within the specified values?

0.8-25 ohms

Go to Step 4

Go to Step 11

4

With a DMM mesure the resistance of the transfer case lock solenoid, by probing the lock solenoid control circuit and the ignition 1 circuit

Is the resistance within the specified values?

18-25  ohms

Go to Step 5

Go to Step 11

5

  1. Start the engine and set the parking brake.
  2. Place the vehicle in neutral and depress the brake pedal.
  3. Disconnect the encoder motor connector at the transfer case.
  4. Connect a DMM to the motor control A cicuit at the encoder motor connector, on the module side of the harness, and take the other lead to ground.
  5. With a scan tool command motor control A ON.

Is battery voltage present?

--

Go to Step 6

Go to Step 7

6

  1. Withe the encoder motor connector still disconnected. Connect a DMM to the motor control B circuit at the encoder motor connector, on the module side of the harness
  2. With a scan tool command motor control B ON.

Was battery voltage present?

--

Go to Step 8

Go to Step 7

7

Test motor control A or motor control B circuits for an open or high resistance.

Was the condition found and corrected?

-

Go to Step 13

Go to Step 12

8

  1. Disconnect the encoder motor harness from the transfer case.
  2. Test the 8 volt reference signal on the module side of the harness.

Was the voltage within the specified range?

7-9 V

Go to Step 9

Go to Step 10

9

Check the voltage on the encoder signals P, A, B, and C on the module side of the harness.

Are they within the specified values?

4.8-5.1 V

Go to Step 10

Go to Step 12

10

With the ignition OFF test the encoder signal ground for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Was the condition found and corrected?

--

Go to Step 13

Go to Step 11

11

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

Is the repair complete?

--

Go to Step 13

--

12

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

Is the repair complete?

--

Go to Step 13

--

13
  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