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Q: 4wd does not work on 1999 GMC Sierra 1500

the 4wd servise light is on and none of the 4wd switch bottons work. not even the light to tell u if your in 2wd or 4wd hi or lo..... have replaced the switch and checked the fuses and still nothing.... could use some help...... could it be the tccm? ( transfer case control module) thx
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I had the same problem and no its not the tccm. Its the Encoder Motor Sensor. It gives the biggest headache but the $90 dollar part will get rid of your headache!! I have a 2005 GMC Sierra 1500 Z71 that had the same prob. Will you truck sometimes start out in 4 low? Do you have to turn it off and back on a couple of times for it to get back into 2 wheel drive? If this happens then it is without a doubt that sensor! Its inside the tccm and not too difficult to change out! Hope this helps!
Did this fix your problem. I have the same truck and same problem, except it is getting worse!! I just don't want to trust the dealership and have them charge me an outrageous price. Thanks
I have a 2002 same thing, would not change out of 4 wheel low, no indicator light working on dash for buttons. saw where the pulling the atc fush (20amp) would reset it. checked the fuse and it had blown, replaced it and it works fine now.
On my 1992 the activator power source gets clogged up so I wired it direct to a toggle switch now I just flick the toggle an it comes on I have not had a problem with this in 2 years
I just replaced that as my 4wd service light came on as well. Took to the dealer and that is what was wrong. $800 repair at the dealer
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