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.Google+
Car Problem Reports
GMC Yukon XL 1500 4WD Transfer Case Position Sensor/Selector Switch May Fail
GMC Yukon XL 1500 Problem
Drive Train Affected: 4WD
Average Mileage: 111,394 mi (19,000 mi - 205,000 mi)
Visitor, 2001 GMC Yukon XL 1500, 4WD, 136,000 mi
Gets stuck in 4 wheel drive and does not return to 2 wheel main driving position
Can't shift into 4 wheel drive without getting stuck in. 4 wheel drive
Visitor, 2005 GMC Yukon XL 1500, 4WD, 100,000 mi
When I start my 2005 GMC Yukon, it will often times, by stuck in 4WD and won't switch to 2WD when I push the 2WD button. I've changed the actuator, but it's still stuck in 4WD. I've already purchased the encoder ring, but, after watching an installation video on "YOU TUBE," it talks about RE-PROGRAMING the encoder ring. How in the heck is this a DIY project if I don't have the computer programing equipment?!!
Visitor, 2003 GMC Yukon XL 1500, 4WD, 95,000 mi
it would switch into 4WD on it's own and I couldn't get it switched back to 2WD. It did this randomly. I took it in for repair...I had an extended warranty. They said it wasn't covered. Had to replace the Transfer Case control module sensor. I think it should be covered...nothing I could have done to prevent this.
Visitor, 2005 GMC Yukon XL 1500, 4WD, 82,000 mi
Getting SERVICE 4WD on cluster. All lights out sometimes on push button control. Bulb test passes. Has gone into 4WD LO mode by itself. Can't change drive mode. Problem and message will go away for weeks sometimes.
Visitor, 2005 GMC Yukon XL 1500, 4WD, 124,000 mi
Yukon would switch itself into 4wd from 2wd.
My wife figured out how to turn off the ignition and get it back into 2wd again.
Glad to know that its the sensor that needs to be replaced.
Visitor, 2005 GMC Yukon XL 1500, 4WD, 78,500 mi
upon starting, 4wd low is already engaged, difficult switching out of low. has happened twice.
Visitor, 2005 GMC Yukon XL 1500, 4WD, 75,000 mi
intermittent "service 4wd" message resulting in total outage of 4wd and even involuntary shifting into 4wd Low.
Visitor, 2000 GMC Yukon XL 1500, 4WD, 205,000 mi
used to stick in 4 WD Now it wont go in 4 WD atm all
Visitor, 2005 GMC Yukon XL 1500, 4WD, 126,000 mi
Same as previous posters. Intermittently goes into 4-Lo. This is a safety hazard, and another thing for GM to be ashamed of about this particular vehicle, which is both the worst AND most expensive I've ever owned!