First off I'd just like to say hello to all the people here, this site is great! I've been reading through just about every 4wd thread but can't find one with my problem exactly. All the lights on my switch stay lit up (see photo). Along with the lights all being on, the car sags and won't accelerate and it shifts erratically like the computer thinks its in 4lo. For the last 2years I have had to drive with the 4wd fuse pulled out for it to drive normally (the fuse from the panel between the driver door and side of the dash).

I have 99 blazer LS, I have the auto 4wd transfer case with the 4-button switch on the dash. My problem was every light on my switch lit up at the same time (see photo attached) and it gave me no response when trying to engage 4wd or any other mode (The service 4wd on the dash is NOT on). I replaced the 4-button switch with a used one and it worked for 20min until i decided to try 4lo and it got stuck in 4lo haha sound familiar? I got it out of 4lo eventually manually with a wrench on the transfer case and I took apart the encoder motor ( I know your not supposed to but it was worth a try because it was corroded and seized) to realign it out of 4lo. After I was finally able to get it back into 2hi (it sat for a few weeks before i got around to it) my new/used switch has all lights lit up again and no response to anything. I don't know if something is shorting out my switch or a bad encoder motor. I gave up and toughed it out in 2wd last winter.

Another note: While it was stuck in 4lo The switch was working intermittently (all lights on sometimes or and all lights off sometimes and when it was working properly only one light was on (blinking) and it was trying to shift) when the switch was working properly I could hear it trying to shift out of it but there must have been too much friction ( due to it never being in 4lo for the 5years i've owned it) to make the shift out of 4lo. I could hear the tccm clicking and all that. I also checked the vacuum actuator under the battery tray, all seemed well it moved freely but I believe this is not the problem or i would be getting some response from my switch now and the front axle just would not be engaging.

This year i've decided to get the 4wd working again, so i replaced the encoder motor with a good used one. I'm pretty sure it was good because a buddy replaced his motor and it didnt fix his 4wd problem until he replaced something else, not sure what it was (he kept the new motor in and gave me the used one). Long story short I replaced the encoder motor this last sunday and nothing changed. I will try and unplug the TCCM on mine and see if that will fix it. Otherwise i guess i will try and buy a new switch again seeing how that fixed it the first time until i got it in 4lo last season. Hopefully i don't have something shorting my switch out and my money goes down the drain on a new switch again (would make it my 3rd switch).

So today I unplugged the TCCM under the passenger kick panel and all the connectors looked good, not corroded. Just a little tinge of blue on one of the 4-pin prongs. I disconnected it and cleaned all the prongs with alcohol and a swab, put dialectric grease on all prongs and it still didn't fix my problem. I don't need to pull the tccm fuse to reset it if I unplugged it I assume? I don't see a fuse or relay for 4wd under the hood. Is there one? Or is it just the 10amp fuse on the left side of my dash? I'm starting to think that I might have a bad TCCM. I'm having trouble finding one with my part # on ebay. Will other numbers work? Sorry for the long post any help to point me in the right direction would be greatly appreciated. Its snowing and the lake effect in Cleveland brings alot of snow! Thanks a lot!

 

The TCCM's for the Blazer have been updated and have a different part number. It should list the part numbers the updated model replaces at least the one I got off ebay did. I am at work and don't have the part number for the new one handy but I am sure someone here will have it. Or do what I did and keep looking, you will find it. I got a killer deal on mine. I think it was around $240 US including shipping to the border which seemed pretty good to me as the dealer here in town wanted $850 bucks for the one he had.

Try part number 12577412 and see if they list your old TCCM.

 

i have the same problem with mine i got a encoder from th junk yard today . did you ever get yours fixed and if so what was the problem mine has the same problems yours did all lights on and shifting funny any info you have would be nice thank you