* A DIAGNOSTIC B+ is a low current circuit that DOES NOT have enough current to light a test light.
* A short to ground on the AWD indicator control circuit will cause the AWD indicator to remain ON at all times.
* An open or high resistance on the AWD indicator control circuit will cause the AWD indicator to be inoperative during the 2 second bulb
inspection.
* An open in the indicator dimming control circuit will cause the 2 High, AWD, 4 High and 4 Low mode indicators to be inoperative during the
2 second bulb inspection.
* The EL-49741 - harness is a good source for 9 V.
* The EL-49742 - harness is a good source for B+ and ground.
* With key REMOVED - opening a door puts a true B+ on the indicator dimming control circuit, TCSCS X1 pin 4. Other possible voltages are
listed below:
- Door open, key removed - indicator dimming control circuit voltage = true B+.
- Door open, key in, key OFF - indicator dimming control circuit voltage = true B+.
- Door open, key ON, engine OFF - indicator dimming control circuit voltage = diagnostic B+.
- All doors closed, key OFF - indicator dimming control circuit voltage = B+ (high current - enough to light a test light).
- All doors closed, key ON, engine OFF - indicator dimming control circuit voltage = diagnostic B+.
- Key ON, engine OFF. Place a shop light on the DRL sensor. When the DRL sensor commands the headlights OFF, the indicator dimming
control circuit voltage, TCSCS X1 pin 4, will go from a diagnostic B+ to a true B+.
Reference Information
Schematic Reference
Transfer Case Control Schematics (See: Transmission and Drivetrain/Transfer Case/Diagrams/Electrical Diagrams/MP 3023/3024-NQH - Transfer
Case)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Electrical Information Reference
* Circuit Testing (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Circuit
Testing/Circuit Testing)
* Connector Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic
Procedures/Connector Repairs/Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (See: Testing and Inspection/Component Tests and General Diagnostics/General
Electrical Diagnostic Procedures/Circuit Testing/Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic Procedures/Wiring
Repairs/Wiring Repairs)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information.
Special Tools
* EL-49741 - 9 V+ Power Source Harness
* EL-49742 - Battery Voltage B+ and Ground Source Harness
* J 35616 - GM-Approved Terminal Test Kit
Circuit/System Verification
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).
2. Door Open, key ON, engine OFF.
3. Using the L-BU probe J 35616-64B, test for a diagnostic B+ (+0.0/-1.0 V) between the indicator dimming control circuit, TCSCS X1 pin 4
and a good ground, such as the ground terminal of the EL-49742 - harness, black terminal.
锟斤拷 If the voltage is less than the specified range, test the affected circuit for an open/high resistance, short to ground, or short to voltage. If all
circuits and connections test normal, test the body control module (BCM) for proper operation.
4. Using the L-BU probe J 35616-64B, test for a diagnostic B+ (+0.0/-1.0 V) between the indicator dimming control circuit, TCSCS X1 pin 4
and the AWD indicator control circuit, TSCSC X1 pin 7.
锟斤拷 If the voltage is less than the specified range, test the AWD 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.
