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B0790




DTC B0790

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC B0790
- Transfer Case Neutral Indicator Circuit Malfunction

Diagnostic Fault Information





Circuit/System Description

The Neutral indicator control circuit consists of an ignition 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 voltage circuit, traveling through the Neutral indicator LED, at which time the transfer case shift control module (TCCM) supplies the ground through the Neutral indicator control circuit.

Conditions for Running the DTC

* Ignition ON.
* System voltage 9-18 V.

Conditions for Setting the DTC

* The system monitors the voltage on the Neutral indicator control circuit.
* If the TCCM detects 3.5 V or less when the Neutral indicator is commanded OFF, the DTC is logged.
* If the TCCM detects 3.5 V or more when the Neutral indicator is commanded ON, the DTC is logged.

Action Taken When the DTC Sets

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

Conditions for Clearing the DTC

* The TCCM clears the DTC once the conditions for setting the DTC no longer exist.
* A history DTC will clear after 33 consecutive ignition cycles without a fault present.
* History DTCs can be cleared using a scan tool.

Diagnostic Aids

* A TRUE B+ has enough current to light a test light.
* A DIAGNOSTIC B+ is a low current circuit that DOES NOT have enough current to light a test light.
* An open on the ignition voltage circuit will cause the 4WD HI, Neutral, 4WD HI Locked, 4WD LO Locked, Differential Lock Front, and Differential Lock Rear mode indicators to be inoperative during the 2 second bulb inspection.
* A short to ground on any of the mode indicator control circuits will cause that indicator to remain ON at all times.
* An open or high resistance on any of the mode indicators will cause that indicator to be inoperative during the 2 second bulb inspection.
* EL-49741 - harness is a good source for 9 V.
* EL-49742 - harness is a good source for B+ and ground.

Reference Information
Schematic Reference

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

Component Connector End Views (Connector End Views By Name)
Description and Operation

Transfer Case Description and Operation (Description and Operation)
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.

Circuit/System Verification

1. Verify that the TCCM switch fuse, fuse 58 underhood fuse block, is NOT open.

• If the TCCM switch fuse is open, test the ignition voltage circuit, transfer case shift control switch (TCSCS), TCSCS harness X1 pin 7, for a short to ground. The TCSCS is also known as the accessory or multifunction I/P switch.

2. Key ON, engine OFF. The TCCM runs a 2 second bulb test on all indicators of the TCSCS at key ON.

Circuit/System Testing

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

1. Remove key. Disconnect the X1 connector at the transfer case shift control switch (TCSCS), also known as the accessory or multifunction I/P switch.
2. Key removed. Using the L-BU probe J 35616-64B, test for a true B+ (+0.0/-1.0 V) between the ignition voltage circuit, TCSCS X1 pin 7 and a good ground, such as the ground terminal of the EL-49742 - harness, black terminal.

• If the voltage is less than the specified value, test the affected circuit for an open/high resistance or short to ground. If all circuits and connections test normal, refer to Wiring Systems and Power Management.

3. Using the L-BU probe J 35616-64B, test for a diagnostic B+ (+0.0/-1.0 V) between the ignition voltage circuit, TCSCS X1 pin 7 and the following TCSCS X1 circuits. (The control circuit for the mode/range that the transfer case currently is in should test as a true B+.)

* Neutral Mode - Control circuit pin 10
* 4 HI Mode - Control circuit pin 11
* 4 HI Locked Mode - Control circuit pin 9
* 4 LO Locked Mode - Control circuit pin 1
* Differential Lock Front Mode (G93) - Control circuit pin 17
* Differential Lock Rear Mode (G93) - Control circuit pin 8

• If the voltage is less than the specified value, test the affected 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 ohm between the ignition voltage circuit, TCSCS X1 pin 7 and all other pins of the TCSCS X1 except the other ignition voltage circuit pin 5.

• 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. Using the L-BU probe J 35616-64B, test for greater than 10 ohm between the neutral indicator control circuit, TCSCS X1 pin 10 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.

6. Test the TCSCS for proper operation.

Component Testing

TCCM
1. Key OFF. Disconnect the X1 connector at the TCSCS.
2. Key ON, engine OFF.
3. Using the L-BU probe J 35616-64B, test for 4.5-5.5 V between the 5-volt reference circuit, TCSCS harness X1 pin 16 and a good ground.

• If the voltage is greater than the specified range, test the 5-volt reference circuit for a short to voltage. If all circuits and connections test normal, replace the TCCM.
• If the voltage is less than the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If all circuits and connections test normal, replace the TCCM.

4. Using the L-BU probe J 35616-64B, connect a test light between the 5-volt reference circuit, TCSCS harness X1 pin 16 and a good ground. The test light should illuminate dimly.

• If the test light does not illuminate, obtain a different test light and repeat step 4.

5. Using the L-BU probe J 35616-64B, connect a test light between the TCSCS harness as specified below for the LED control circuit being tested.
6. Key ON, engine OFF.
7. Using the Special Function ability of the scan tool, command the affected LED ON and OFF. The test light should turn ON and OFF as commanded.

• If the test light remains illuminated when commanded OFF, test the affected control circuit for a short to ground. If all circuits and connections test normal, replace the TCCM.
• If the test light remains OFF when commanded ON, test the affected control circuit for an open/high resistance or short to voltage. If all circuits and connections test normal, replace the TCCM.





TCSCS - Accessory / Multifunction I/P Switch
1. Using the L-BU probes J 35616-65B, connect the 9 V power source EL-49741 - harness 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 9 V power source EL-49741 - harness.
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/Accessory Switch.





Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests)

* Transfer Case Shift Control Module Programming and Setup (Programming and Relearning)
* Transfer Case Shift Control Module Replacement (Service and Repair)
* Transfer Case Shift Control Switch Replacement (Service and Repair)

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