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GMC Expert
GMC Expert, ASE Certified Technician
Category: GM
Satisfied Customers: 10370
Experience:  30 yrs experience, ase certified, shop owner
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1999 gmc: wheel drive..locking..hear the transfer case motor working

Customer Question

1999 gmc jimmyXXXXXnot locking push 4 wheel high or low or auto and light just blinks you can hear the transfer case motor working
Submitted: 7 years ago.
Category: GM
Expert:  GMC Expert replied 7 years ago.

hi there is a few things that can cause this , the control module , the encodermotor ,and others here are some tests to do and let me know what you find

Tests/Procedures:1. Disconnect the module from behind the right-hand kick panel. Verify no corrosion, inspect carefully the terminals in the connector and the module. Listen carefully to the transfer case encoder motor and internal transfer case. If the transfer case is shifting, proceed with step 8. If there is no activity from the transfer case, proceed with step 2.

2. Jump the Tan (1569) wire at terminal E1 of the large connector to ground. An audible click should be heard from the encoder motor on the transfer case.

3. Jump the Orange (1640) wire at terminal D to the Red (1553) wire at terminal B of the 4 terminal connector.

4. Jump the Black (2150) wire at terminal C to the Black (1552) wire at terminal A.

5. Check for the transfer case to shift. Reverse polarity of the Red (1553) and the Black (1552) wires, and check for the transfer case motor to change directions.

6. If the transfer case does not shift, repeat the procedure using the same wire colors at the motor on the transfer case.

7. If the operation is ok, reconnect the module, back probe the Red and Black wires at terminals A and B. Expect voltage to appear across the 2 wires when selecting a mode shift. The module should click and apply power and ground to the 2 wires. If voltage is leaving the Transfer Case Control Module, replace.

8. Locate the vacuum solenoid on the firewall. Verify engine vacuum to one side of the solenoid. WhenXXXXXis selected, the solenoid is energized allowing vacuum to pass through the solenoid. Jump the solenoid vacuum hoses and verify the front axle engages, use a mirror and flash light to view the servo under the battery.

9. Install a test light across the 2 solenoid wires and check for the test light to come on whenXXXXXis selected.
Potential Causes:Encoder Motor
Transfer Case Control Module (TCCM)
Tech Tips:A blinking indicator means the module waiting forXXXXX Verify if the module clicks, transfer case makes and mode shift and the front axle is engaged.