I've had this on going issue since the truck had 70,000 miles. every once in a while I would get this service 4x4 light. but when I shut off the truck it would not come back on for 6-8 months. If I tried to engage the 4x4 by pushing the button when the service light was on, it would not engage, if I turned the truck off and started it back up the light would go off and the 4x4 would work just fine.

Everyone I know who have identical trucks say they had the similar problems and the service dealers said it was the switches and had them replaced under warranty. Is this a recalled Item? Is there other simple things, vacuum lines, fuses. anything?

Thanks
Jason

GM used several mechanisms to engage the front transfer case and hubs. It could be either that is dorking up. Some vehicles have a vacuum system, and others use an electronic solenoid plunger that engages the front system. I have seen both fail.

If you shoot a PM to R Addiction / John, he can probably tell you exactly where/what to check. He is a Mr. Goodwrench.

There are 3 major components that control 4wd on the newer chevys assuming you have auto trac. Encoder motor on transfer case I see bad about 80% of time,around 450-500$ for the part,transfer case control module ,around 400-500$ for part,rarely bad,dash switch,around 45 or 50$,once in a while you get lucky and thats it, 4wd actuater on front axle,130-150$,rarely see bad ones on 99 and newer new style chevys,the old 88-mid 90's they went bad all the time and you retrofitted the new style one along with a new wiring harness. Is your truck a old style 99 or new style 99? I have a new in the box transfer case controller that DIDN'T fix a truck we thought it would that fits the 99 new style that cost us 380$ or 420$ wholesale 2 years ago if you'd like to try it,I could send it your way,Smitty

If your ever in my neck of the woods I could scan it for free too,Smitty

It is the new style '99. and I forgot about the scanning of the computer. I will be going down to auto zone on lunch to have it scanned for free. They have diagnosed a few things for me. I'll let you know about the transfer case controller. That just might be it, some times when I am driving around 10 mph in 2HI it will want to switch to 4LO. The light will be flashing 4LO. So I would switch it to auto-trac and get to 30mph and switch back to 2HI. This just started to happen last week.

Is there a way I can put my truck into 4x4 manully? I need to get back to my boat that is in some sand?

I'm not sure if Autozones scanner reader will look at the transfer case module the same as a snapon mt-2500. If you need any further help let me know,my scanner has transmission troubleshooter which will show a path of trouble shooting and testing. The t-case module on your truck is buried deep under the dash near the firewall/top of steering column. If you pull the headlight swith panel out you can see it way in there,if you rap on it with a 3/8" extension or similar and it starts working again for a little while it is the module. There is no real way to manually get truck into 4wd other than pulling the front driveshaft then the encoder motor on t-case then rotate the shaft under neath it with something in the slot but it would be a bad idea as it holds everything in place,Smitty