GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC K Pickup - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 243-NP1 (Two Speed 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 transfer case motor/encoder will rotate clockwise or counterclockwise in order to shift to the proper gear. If the transfer case shift control module does not see the following conditions the switch indicator lamps will continue to flash.

    • Motor/Encoder has driven to the proper gear position.
    • The front axle switch is closed (received by a signal from the PCM).
    • The vehicle is not moving (received by a signal from the PCM).
    • The Park/Neutral switch has closed or the clutch pedal is fully depressed (providing a ground to the TCCM).

Test Description

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

  1. This step tests the operation of the transfer case shift control switch to help determine if the system is operating properly.

    2.

  2. This step determines if the vehicle speed sensor reading is correct.

    3.

  3. This step tests the operation of the front axle switch/actuator state.

    4.

  4. This step determines if the park switch reading is correct.

Switch Indicator Lamps Flash Continuously

Step

Action

Value(s)

Yes

No

1

Did you perform A Diagnostic System Check - Transfer Case?

--

Go to Step 2

Go to Diagnostic System Check - Transfer Case

2

  1. Start the engine.
  2. Place the transmission into NEUTRAL.
  3. Set the park brake.
  4. Depress each of the shift control switch buttons.

Does the transfer case range change with the press of all of the shift control switch buttons?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Install a scan tool.
  3. Use the scan tool in order to read the vehicle speed sensor on the Engine Control Data Lists.

Is the vehicle speed sensor within the specified range?

0 MPH

Go to Step 4

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0L and 5.7L

4

  1. Turn ON the ignition, with the engine ON.
  2. Use the scan tool in order to read the Front Axle Switch on the Engine Control Data Lists.
  3. Place the transmission into NEUTRAL.
  4. Set the park brake.
  5. Depress the 4WD shift control switch button.

Does the Front Axle Switch state change from UNLOCKED to LOCKED?

--

Go to Step 5

Go to Front Axle Will Not Engage

5

Observe the position of the park/neutral switch.

Does the park/neutral switch operate properly?

--

Go to Step 6

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0L and 5.7L

6

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

Did you complete the replacement ?

--

Go to Step 7

--

7

Operate the vehicle within the conditions for causing the symptom as specified in the supporting text.

Does the symptom re-occur?

--

Go to Step 2

System OK