4WD Service Light and No more Reverse.

BigLurr54 · December 22, 2013

I loaded the family in to the 2001 Yukon XLtoday to go over to my parents house for our Christmas and I had no reverse. The Service 4WD light came on for the first time since I have had the truck. I had forward and I had park but when in neutral there was a slight whirling noise near the transfer case. None of the lights on the 4wd buttons were lite up.

A two weeks ago we had a snow storm come through and i parked the yukon on a hill to get it out of the way of the plow. I had put it in 4 lo to climb up the steep snowy hill. Two days ago I pulled the truck off the hill. When i was parking the truck I got it rolling then shifted to neutral and then pushed 2wd. The truck rolled a bit but then it stopped before the transfer case could switch. I tried again and had the same issue with it stopping before it switched. Now the truck was in its parking spot and i couldnt go forward any more so i shut the truck off and figured i would wait until i drove it next when i have room to get the truck moving.

After christmas at my parents I pulled the truck out of the parking spot and drove it down the road a bit to see if i could get it to shift into 2 wd. I had no luck. I put the truck in park and it didnt have park anymore. I still had drive. I gassed it to see what tires spun free and it was in 2 wd. I pulled back up to the house and parked it and it went into park. I still have no reverse and I have no indicator lights on the switches. I checked the Transmission fluid and it was clean and smelled sweet.

Any ideas where to go with this? Anyone else find it funny that we have to be afraid of putting our trucks in 4wd? Im ready to go back to my old 1989 Suburban. The ride is a little rougher but the dependability is un-matched.

gmtech4 · December 22, 2013

wow ,this is the strangest thing ive heard ,,,,,

shifting in and out of 4lo HAS to be shifted while the transmission is in neutral and veh slightly moving ,,,

that said ,,the DIC message means there is a diagnostic trouble code (DTC),,,,it has to scanned ,,,,you get that code ,,,post back what that code is and we can help

try the shifting proper thing also ,,,ya still have a code but no reverse makes no sense at all

merry xmas !!!

goatboy0067 · January 1, 2014

sorry to hear of your troubles i have the same issue only they happened at seperate times . first the neutral saftey back up switch went this is the electronic switch on the trans that tells it what to do. mine didnt light up when i tried to shift into gear and wouldnt engage the trans this is due to water getting into the unit and corroding the contacts or water filling up the switch ( mine just got water in the switch so when it dried i worked properly) i replaced mine it was easy. next i have the same issue with my dic service 4wd still searching for an answer as it didnt throw a code i think it is another water issue or somthing minor. i disconnected the battery and the 4wd worked fine for 2 days then the light returned i also checked the fluid and it was full and was replaced 10,000 miles ago but i did just turn 150000 miles on the od so i was thinking it was a reminder good luck and i will be checking back to see if you got an answer also will post if i figure it out.

BigLurr54 · January 10, 2014

Well I lost forward, parking, and reverse now. There is a grinding noise when i try to put the truck back into park. Like the transfer case is in neutral and theres nothing to stop the trans from spinning.

I did an ohm test on the switch and that all came in spec. My next thing to try is to lift the truck and manually engage the transfer case. My plan is to remove the encoder motor and manually shift the lever. I have a few questions about this.

What is the sequence for the shift lever on the transfer case? ie: all the way down 2w, up one auto.up again 4 hi, up again 4 low, up last time neutral. ... Im sure thats not the correct way.

Once i manually engage the transfer case, I plan to start the truck and see if I get forward or reverse to rule out a blown transfer case and diagnosis it as an encoder motor. Can I do this or will it cause computer issues?

Since I can't drive the truck its hard to bring it in to have the tccm scanned.

BigLurr54 · January 11, 2014

Ok I switched the buttons with my fathers buttons. Same truck. Still nothing. I tolled the truck to flat ground got the 4 wheels up in the air. Rolled in the three inches of mud. Pilulled the drive shaft pulled the encoder motor. Manually shifted the transfer case to a different position and started the truck put it in drive and I had forward reverse and park. I dropped the truck and sure enough it drives. There's a slight grinding noise going into park. My guess is the t case is in 4 hi and the front is still spinning with out the drive shaft so it grubda going into park because there's nothing to stop it from spinning.

Next order of business is order a new encoder motor and pray its not the tccm.