GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 226-NP8 🢒 DTC B0775

Circuit Description

The 4HI indicator circuit consists of an LED dimming supply circuit and a 4HI indicator control circuit. When the 4HI mode is selected, current is supplied to the 4HI indicator by the LED dimming supply circuit, traveling through the 4HI indicator LEDs, at which time the transfer case shift control module supplies the ground through the 4HI indicator control circuit.

Conditions for Running the DTC
    • The ignition is ON.
    • System voltage is 9-18 volts.

Conditions for Setting the DTC
    • The system monitors the voltage on the 4HI indicator control circuit.
    • If the system detects a voltage of 3 volts or less for 1.5 seconds when the 4HI indicator is not commanded, the DTC is logged.
    • If the system detects a voltage of 4.5 volts or greater when the 4HI indicator is commanded, the DTC is logged.

Action Taken When the DTC Sets

The SERVICE 4WD indicator remains illuminated for the remainder of the current ignition cycle.

Conditions for Clearing the DTC
    • The transfer case shift control module clears the DTC if the condition for setting the DTC is not currently present.
    • A history DTC clears after 100 consecutive ignition cycles without a fault present.
    • History DTCs can be cleared using a scan tool.

Test Description

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

  1. This step looks for the visual operation of the 4HI indicator. Command both the ON and OFF states.

    2.

  2. This step helps determine if proper voltage is supplied to the transfer case select switch.

    3.

  3. This step helps determine if there is a short to ground in the indicator control circuit.

    4.

  4. This step helps determine if there is an open in the indicator control circuit.

    5.

  5. This step tests the indicator feed circuit for an open or high resistance.

    6.

  6. This step tests the 4HI neutral control circuit for a short to ground.

    7.

  7. This step tests the 4HI neutral control circuit for an open or high resistance.

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

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. With the scan tool, command the 4HI indicator control ON and OFF.

Does the 4HI neutral turn ON and OFF with each command?

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

Go to Step 3

3

With a scan tool, command the AWD, 4LO, and 2HI indicators ON and OFF.

Do all the indicators turn ON and OFF?

Go to Step 4

Go to Step 6

4

Does the 4HI indicator stay ON?

Go to Step 7

Go to Step 5

5

  1. Remove the transfer case select switch.
  2. While the transfer case select switch is still connected to the harness, backprobe the 4HI neutral control circuit with a wire to a good ground.

Does the 4HI indicator illuminate?

Go to Step 8

Go to Step 9

6

Test the LED dimming supply circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 9

7

Test the 4HI indicator control circuit for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 11

Go to Step 10

8

Test the 4HI indicator control 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 10

9

Replace the transfer case select switch. Refer to Transfer Case Shift Control Switch Replacement .

Did you complete the repair?

Go to Step 11

--

10

Important : After transfer case shift control module replacement and reprogramming, ensure all doors are closed and the key is out of the ignition, then open and close the doors again and wait 2 minutes to avoid incomplete programming or false communication DTCs.

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 11

--

11
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC set?

Go to Step 2

System OK