GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Envoy - 4WD 🢒 Driveline/Axle 🢒 Transfer Case - NVG 226-NP8 🢒 DTC B0790

Circuit Description

The neutral indicator circuit consists of an ignition 3 voltage circuit and a neutral indicator control circuit. When the neutral mode is selected, current is supplied to the neutral indicator by the ignition 3 voltage circuit, traveling through the neutral indicator LED, at which time the transfer case shift control module supplies the ground through the neutral indicator control circuit. This DTC detects an open, short to ground or a short to voltage.

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 neutral indicator control circuit.
    • If the system detects a voltage of 3 volts or less for 1.5 seconds when the neutral indicator is not commanded, the DTC is logged.
    • If the system detects a voltage of 4.5 volts or greater when the neutral 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 neutral indicator. Command both the ON and OFF states.

    2.

  2. This step tests for voltage at the neutral indicator feed side of the transfer case select switch.

    3.

  3. This step verifies that the transfer case shift control module is providing ground to the neutral indicator.

    4.

  4. This step tests if ground is constantly being applied to the neutral indicator.

    5.

  5. This step tests the control circuit of the neutral indicator for a short to voltage or an open.

    6.

  6. This step tests the control circuit of the neutral indicator for a short to ground.

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 neutral control ON and OFF.

Does the neutral control turn ON and OFF with each command?

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

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Remove the transfer case select switch.
  3. Disconnect the connector on the transfer case select switch.
  4. Turn the ignition ON.
  5. Probe the ignition 3 voltage circuit with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the harness connector of the neutral indicator control circuit and the neutral indicator feed circuit.
  2. With the scan tool, command the neutral indicator ON and OFF.

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the neutral indicator control circuit for a short to voltage or an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuit of the neutral indicator 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 13

Go to Step 9

8

Inspect for poor connections at the transfer case select switch. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the transfer case shift control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the ignition 3 voltage circuit of the transfer case select switch for an open, high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

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

Did you complete the repair?

Go to Step 13

--

12

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 13

--

13
  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