* Transfer Case Control Schematics (See: Transmission and Drivetrain/Transfer Case/Diagrams/Electrical Diagrams/MP 3023/3024-NQH -
Transfer Case)
* Engine Controls Schematics (See: Diagrams/Electrical Diagrams/Powertrain Management/System Diagram)
Connector End View Reference
Component Connector End Views (See: Diagrams/Connector Views)
Description and Operation
Transfer Case Description and Operation (See: Transmission and Drivetrain/Transfer Case/Description and Operation/MP 3023/3024-NQH -
Transfer Case/Transfer Case Description and Operation)
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)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (See: Diagnostic Trouble Code Descriptions/Powertrain Diagnostic Trouble Code
(DTC) Type Definitions)
Scan Tool Reference
Control Module References (See: Testing and Inspection/Programming and Relearning) for scan tool information
Special Tools
* EL-49742 - Battery Voltage B+ and Ground Source Harness
* J 35616 - GM-Approved Terminal Test Kit
Circuit/System Verification
1. Raise and support the drive wheels.
2. Start and idle the engine.
3. Place the transmission in DRIVE.
4. Monitor VSS on the scan tool under engine data.
5. The VSS on the scan tool should be greater than 100 RPM.
Circuit/System Testing
1. Key OFF. Let sit for 2 minutes to ensure that the ECM shuts down.
2. Disconnect the X1 connector from the VSS. Using the J 35616-2A GY probes, test for less than 0.1 V between the following circuits and a
good ground.
* VSS high signal circuit, VSS harness X1 pin A.
* VSS low signal circuit, VSS harness X1 pin B.
锟斤拷If the voltage is greater than the specified value, test the affected circuit for a short to voltage. If all circuits and connections test
normal, test the ECM for proper operation.
3. Key ON, engine OFF. Test for a diagnostic 2-3 V (low current) between the following circuits and a good ground.
* VSS high signal circuit, VSS harness X1 pin A.
* VSS low signal circuit, VSS harness X1 pin B.
锟斤拷If the voltage is less than the specified value, test the affected circuit for an open/high resistance, short to ground or short together. If
all circuits and connections test normal, test the ECM for proper operation.
锟斤拷If the voltage is greater than the specified value, test the affected circuit for a short to voltage. If all circuits and connections test
normal, test the ECM for proper operation.
4. Test the VSS for proper operation.
