GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 TopKick C-Series (Conventional) C4/C5 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 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 has been selected by the driver, 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.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B0790 Transfer Case Neutral Indicator Circuit Malfunction

Conditions for Running the DTC
    • The ignition is ON.
    • The 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 more when the Neutral indicator is commanded, the DTC is logged.

Action Taken When the DTC Sets

The SERVICE 4WD indicator is not illuminated.

Conditions for Clearing the DTC
    • The transfer case shift control module will clear the DTC if the condition for setting the DTC is not currently present.
    • A history DTC will clear 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 inspects 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 - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. With the scan tool, command the Neutral Indicator Light ON and OFF.

Does the Neutral Indicator Light turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections

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 DMM that is connected to a good ground.

Does the DMM indicate battery voltage?

Go to Step 4

Go to Step 10

4

  1. Connect a DMM between the harness connector of the Neutral indicator control circuit and the ignition 3 voltage circuit.
  2. With the scan tool, command the Neutral indicator light On and Off.

Does the DMM indicate battery voltage and then 0 volts with each command?

Go to Step 8

Go to Step 5

5

Does the DMM continue to indicate battery voltage 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 .

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 .

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8
  1. Disconnect the transfer case shift control module connectors C1 and C2.
  2. Inspect for poor connections at the transfer case shift control switch. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs .

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 .

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 .

Did you complete the repair?

Go to Step 13

--

11

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

Did you complete the repair?

Go to Step 13

--

12

Replace the transfer case shift control module. Refer to Control Module References for replacement, setup, and programming.

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