99' Blazer....for awhile the 3 way dash lights work, don't work. Sometimes when they work they still don't engage the TCM....sometimes you have to hit 4 lo, then hit 4 hi and then it will kick in. Sometimes 4 lo gets stuck and takes a couple days sitting before it kicks out....then nothing works, no lights, no TCM working...once when it locked into 4 lo I took battery out and the vacum was working and still sucked in. So I decided why not tie back the vacuum cable so the front axles are locked in....that would make it a 4x4 all the time....?....I think I'm wrong because the cable is tied back but its still not in 4x4...BUT....my dash switch light are working, and when I click to 4 lo, 4 hi or 2 wheel it lights up and clicks the TCM.....so I don't think I have a bad switch, or a bad TCM.....so is my transfer case bad? Or do the vacum lines and perhaps the vacuum switch on the case need replaced...?

 

First place to look for problems in these is the vacuum system. I had the same issues with mine, sometimes I would have lights and other times I wouldn't. My front axle was not engaging though. So I replaced all the vacuum lines and that fixed the actuator, than I took the tccm out of the passenger side kick panel and cleaned all the terminals really well, there was some corrosion in there. That seemed to help as well but my lights were still acting kind of funky. So I pulled the switch out of the dash and opened it up, I noticed the solder joints on the back were cracked, so I re-solder all the joints I could and that seems to have fixed my issues with it.

 

Sounds like there might be a bind in transfer case, I had a similar problem on a 99. I removed encoder motor and used a large crescent to move shaft on t case you may find its a little bound up took me 5 minutes to even get mine to go in to 4lo. As you move position to position it should start freeing up(less resistance to shift).If you have your vacume actuator still pulled in via zip tie you can leave front end on jack stands or lift and spin front tire to see if it locks in. Also it would be a great time to check encoder motor make sure it moves while you have it off t case. They are know to be a common problem in blazers. If you cant get front to lock check cable from actuator to front diff if that's not it, its probably time to drain t case and have a look at the fluid to see if its gone bad. Hopefully this is helpful, if any questions ask please.

 

take a look through here

 

Thanks guys...I also read that link and said to pull and clamp the actuator cable to see if I have 4 wheel drive, which I did and its not in 4 wheel.....but it didn't give any info what to do next....but your response gives me and idea what to try. Sounds like either the front axle isn't locking or transfer case isn't engaging...if I figure that out then I'll worry about the vacuum lines later...it still does great in snow.....but man I need it when it gets really deep or black ice.

 

I just put in garage, still have the actuater cable pulled, with it started and in park I got under and turned the front drive shaft....it will not turn. So I assume the tranfer case is working and engaged in 4x4, but for some reason the front axle is not locking end, but will double check by jacking up and seeing if the front wheels turn.

 

may need to make sure the cable is pulled far enough, I believe they need to pull out anywhere from 1/2 to 3/4" to lock in all the way. Could be that the cable is not connected inside the front dif, I dont think that is a very common issue tho.

 

Well both front tires spin freely...I don't think thats good since its in 4 hi, actuater pulled out, and transfer case locked in 4x4......at a stand still. Guessing faulty axle somehow, something got sheared off...? Is there some electronic wiring that runs from the front axle to the tccm that I'm not aware of....my belief is that the acuater cable locked in the front axle and nothing else.

 

Its seems to pull in a good 1/2"....but perhaps something is wrong at the end that goes into the axle....at least I think I'm getting it narrowed down.

 

I would pull cable off front axle side first to see if its moving (not snapped or rusted up)and still attached. Then decided if its axle problem. The cable locks the front diff electricial connector is for indicator light on switch I believe.