The 4WD transfer case encoder motor position sensor or the selector switch may fail causing the service 4WD message to be displayed. Fault code(s) stored in the transfer case control module will be of assistance in determining the exact fault causing the message to be displayed.
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Repairpal verified 1990 Chevrolet Suburban 2500 problems
The rear axle bearings have been known to wear grooves in the rear axle shafts, creating a grinding noise and leaky axle seals. An indication that this problem has occurred is axle fluid leaking onto the wheel.
The pitman arm and/or lower ball joints may wear causing loose steering and alignment issues. Replacement of worn components will be necessary before the alignment can be properly set to specification.