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.
Service 4WD Message May be Displayed on GMC Yukon XL 2500
Average mileage: 69,333 (30,000–110,000)
9 people reported this problem
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The first time this happened, I resoldered the connections on the switch and it worked another two years. Then at the next failure, I replaced the switch. Not hard to do either.
Service 4wd light came on. Replaced encoder motor sensor.