4wd Questions

[67ChevyRedneck]

Two years ago, my "Service 4wd" light came on fairly often. I installed a factory fog light kit and had to have the PCM flashed... after that the light never came on again. I used 4wd a couple times a month to climb a steep grass hill at my apartment after I load all of my dogs stuff when I go on trips. (Carrying two crates/food/clothes up two flights of stairs then out to the parking lot is a PITA so I drive down the hill right to my door )

 

Starting three weeks ago it popped on when I was driving from Greensboro NC to Greenville SC. When I stopped for gas and restarted it went off and stayed off. It came on again friday night after about 20 mins of driving and again last night after about the same amount of time, turning off when the truck is restarted. My drive to work is only 8 miles and it's never come on during a short trip.

 

I spent a couple hours reading posts using the search last night and I still have some questions.

 

Questions:

 

1. Does the transfer case (or even front axle???) have a "low fluid" indicator that would cause the light to come on? (Got 2 conflicting answers in my research.)

 

2. My truck has 110K on it, is there any chance that it is an oil life monitor for the transfer case?

 

3. I also read in my search that 4wd will not engage when the light is on. So I tried it out last night when the light was on, and sure enough, 4wd worked just fine, engaged and disengaged without any funny noises. So, is there really anything wrong? Does that rule out the dash switch as being bad, or is that still possible?

 

4. I took the truck to autozone and they put their OBD II on it to check for codes. There weren't any, but he did say it may not read a non "check engine light code." Is that true? I'd hate to pay GM $80 to use their scanner and no codes show up.

 

5. My truck was originally an Indy truck for about 3 years. Is it possible corrosion is finally playing havoc with my sensors? Is there a diagram somewhere with all of them shown?

 

Thanks for any help. I like to fix my own stuff and I just dropped $900 on new BFG's and Bilsteins two weeks ago and I really don't want to take it to a dealer.

 

Edit: Also, there is no fluid anywhere under the truck. The transfer case is dry, the front Differential is dry, and the CV boots are clean and dry.

[Lincoln30]

I didn't spend nearly as much time analyzing my 99 symptoms when the service 4wd came on my 99. I just replaced the switch and it fixed the problem. The switch was far cheaper then $80 you will pay for diagnostics and takes about 10 minutes to put it. Mine went around the 100K mile mark.

[c4cruiser]

A Service 4WD message in the DIC coupled with the indicator light on the 4WD switch going out and no problems like noise or loss of fluids, typically points to a bad switch assembly. The switch failure was intermittent. Sometimes it would go out for a few miles, sometimes for days. With the switch not lit and the Service 4WD message, the 4WD will not work.

 

That happened to my 99 and I got a new switch for $50 and installed it myself. You only have to pull the trim surround from the dash and remove the screws that hold the switch in place. Disconnec the wire harmess, plug in the new switch, re-attach and replace the trim. Done in about 5 minutes.

 

As far as fluids, my owner's manual has nothing specific about fluid service for either the front diff or the AutoTrac transfer case. I had both changed out at 65K miles and there was nothing that appeared wrong with either fluid. I guess that if you used the 4WD a lot, then it would be reasonable to do more frequest changes especially the front differential fluid. It's cheap and not that hard to do. The blue AutoTrac fluid costs some, but it's certainly worth changing a couple times over the life of the truck.

[67ChevyRedneck]

Thanks Fellas The only difference with mine is that my switch lights never quit working.

 

The switch is at the top of my list before the truck ever sees a GM bay. I also plan on keeping the old girl another 5-10 years, so I'm being a little anal about it

 

Please, if anyone knows more, keep it commin'