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B0790




Transfer Case - MP 3023/3024-NQH


DTC B0790

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (with HP2) (Initial Inspection and Diagnostic Overview)Diagnostic System Check - Vehicle (without HP2) (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptors
DTC B0790 01
- Neutral Indicator Circuit Short to Battery

DTC B0790 06
- Neutral Indicator Circuit Short to Ground or Open

Diagnostic Fault Information





Circuit/System Description

The neutral indicator circuit consists of a light emitting diode (LED), a LED feed circuit and a LED control circuit. The ignition 1 voltage circuit is the LED feed circuit and continuously supplies voltage to the Neutral LED. When the Neutral mode has been selected, the transfer case shift control module (TCCM) provides a ground through the neutral indicator control circuit illuminating the LED. At key ON, the TCCM will illuminate and test each mode indicator for 2 seconds.

Conditions for Running the DTC

* Ignition ON
* System voltage 10-18 V

Conditions for Setting the DTC

* The system monitors the voltage on the neutral indicator control circuit.
* The TCCM detects a voltage of 1.6 V or less for 1.5 seconds when the neutral indicator is commanded ON.
* If the TCCM detects a voltage of 3.4 V or greater when the neutral indicator is commanded OFF.

Action Taken When the DTC Sets

Normal operation, the SERVICE 4WD indicator is commanded ON for the remainder of the ignition cycle. Driver is also informed of fault via bulb inspection.

Conditions for Clearing the DTC

* The TCCM clears the DTC once the condition for setting the DTC no longer present.
* A history DTC clears after 40 consecutive warm-up cycles without a fault present.
* History DTCs can be cleared using a scan tool.

Reference Information
Schematic Reference

Transfer Case Control Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Diagnostic Aids

* A short to ground on the neutral indicator control circuit will cause the neutral indicator to remain ON at all times.
* An open or high resistance will cause the neutral indicator to be inoperative during the 2 second bulb inspection.

Circuit/System Testing

Important: When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J 35616 GM terminal test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.


1. Key OFF. Disconnect the X1 connector at the transfer case shift control switch (TCSCS).
2. Using the L-BU probe J 35616-64B, test for B+ between the ignition 1 voltage circuit, TCSCS X1 pin 2 and a good ground.

• If the voltage is less than the specified range, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, test the body control module (BCM) for proper operation.

3. Using the L-BU probes J 35616-64B, test for B+ between the ignition 1 voltage circuit, TCSCS X1 pin 2 and the neutral indicator control circuit, TSCSC X1 pin 3.

• If the voltage is less than the specified range, test the neutral indicator control circuit for an open/high resistance or short to power. If all circuits and connections test normal, test the TCCM for proper operation.

4. Using the L-BU probe J 35616-64B, test for greater than 10 ohms between the indicator dimming control circuit, TCSCS X1 pin 2 and all other pins of the TCSCS X1.

• If the resistance is less than the specified range, test the affected circuits for a shorted together condition. If all circuits and connections test normal, test the TCCM for proper operation.

5. Disconnect TCCM connector X1.
6. Using the L-BU probe J 35616-64B, test for greater than 10 ohms between the neutral indicator control circuit, TCSCS X1 pin 3 and all other pins of the TCSCS X1.

• If the resistance is less than the specified range, test the affected circuits for a shorted together condition. If all circuits and connections test normal, test the TCCM for proper operation.

7. Test the TCSCS for proper operation.

Component Testing

BCM
1. Key OFF. Disconnect the X1 connector at the TCSCS.
2. Using the L-BU probe J 35616-64B, connect a DVMM between TCSCS harness X1 pin 4 and a good ground.
3. Key ON, engine OFF.
4. Verify that the voltage is greater than 10 V.

• If the voltage is less than 10 V, replace the BCM.

TCCM
1. Key OFF. Disconnect the X1 connector at the TCSCS.
2. Using the L-BU probe J 35616-64B, connect a test light between the TCSCS harness as specified below for the LED being tested.
3. Using the special function ability of the scan tool, command the affected LED ON and OFF. The test light should turn off and on as commanded.

• If the test light does not function as commanded replace the TCCM.





TCSCS
1. Using the L-BU probes J 35616-65B, connect the memory saver harness, EL49741, to the TCSCS as specified below for the LED being tested. Connecting the harness in the opposite pins will not illuminate the LED.
2. Connect a 9 V battery to the memory saver harness EL49741.
3. Verify that only the indicator being tested illuminates.

• If the indicator does not illuminate when tested or the incorrect indicator illuminates, replace the TCSCS.





Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Transfer Case Shift Control Switch Replacement (Without SLT) (Transfer Case Shift Control Switch Replacement (Without SLT))Transfer Case Shift Control Switch Replacement (With SLT) (Transfer Case Shift Control Switch Replacement (With SLT))
* Control Module References (Programming and Relearning) for TCSCM replacement, setup, and programming
* Transfer Case High/Low Clutch Reset (Transfer Case High/Low Clutch Reset)

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