Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Testing
- Remove key. Disconnect the X1 connector at the transfer case shift control switch (TCSCS).
- Door open, key ON, engine OFF.
- 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-49742Β
harness, black terminal.
- 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.
- Using the L-BU probes 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.
- 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.
- Key OFF. Using the L-BU probe J-35616-64B, test for greater than 10 Ξ© between the indicator dimming control circuit, TCSCS X1 pin 4 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.
- Using the L-BU probe J-35616-64B, test for greater than 10 Ξ© between the 4WD HI indicator control circuit, TCSCS X1 pin 7 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.
- Test the TCSCS for proper operation.
When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J-35616Β GM terminal test kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- β’ You smell fuel, burning insulation, or see smoke.
- β’ Brakes feel soft, pull hard to one side, or make grinding noises.
- β’ The engine overheats, stalls repeatedly, or misfires under load.
- β’ You are missing required tools, torque specs, or safe lifting equipment.
- β’ You are not confident in the next step or safety outcome.