Picked up a beautiful 00 zr2 from the original owners summit white black interior 88k miles garage kept it’s a cream puff ! in the ad stated ac does not work or 4wd I’m pretty mechanical not a huge deal to me when I picked it up “service 4wd” was on on the cluster

charged the ac works great!

4wd it’s the 4 button auto I’m new to blazers had a bunch of obs chevys and c10’s

Started by ordering the dash push buttons switch one from Amazon one from Oriley and I checked the solider joints on the original one ….no 4wd… light on the dash was still on “services 4wd”

read to clean the tccm connection did that they all looked good besides the 4 pin had a tiny bit of green on it cleaned it up 4wd worked as normal light went away

less than 24 hours later went to move the blazer and “service 4wd” was back on and no clicking no ticking from the tccm all orange indicator lights out on dash 4wd buttons

I ordered tccm “new reman” from e bay Dorman 599-102

indicator lights came back on the buttons no response from buttons checked all vacuum lines they did not look bad changed 2 I have good vacuum

Put a new vacuum switch on the firewall no different

well must be encoder motor bad ordered one on Amazon 600-901 … installed red light on button’s says neutral messed with it shifts into 4lo only and cannot get out of it …. Cycled key 5 times disconnected battery 30 mins hour and over night no change atc fuse and 4wd fuse good

getting lost here trying to get my buddy with a tech 2 to scan it any thoughts?

and as it is in 4lo now the diaphragm under the battery is not damaged and pulled in and I did check the cable and it moves free

 

Wow, it sounds like you checked everything I can think of.

A thorough check of all possible OBD errors would be appropriate to do.

If no one else has the info, I do have the 99 Service Manual from which I could scan some pages for you in case it helps.

Keep us posted.

 

Have you tried putting the old encoder back into it to see if it will go back into 2wd or any other mode? You might have to manually shift it out of 4LO if it is in 4LO in the transfer case to install the old encoder. That is the next thing I would try anyway.

The 4-button system can be finicky when it comes to parts. Not all of the aftermarket parts are direct replacements for what was in there from the factory and there are A LOT of aftermarket parts that are junk out of the box as well.

 

I actually got two encoder motors off Amazon cuz I thought the first one might be junk I know a lot of these parts after market can be crap it being stuck in 4lo now has the factory encoder motor in it and I have a obd2 scanner and there are no codes codes id like to get my buddy to scan with a tech 2 see what the tccm is doing or if it’s has any codes …. I also read to ground pin 13 on obd2 and the 4wd buttons will flash what codes I dono if it’s true but it dosnt do anything ….. my friend actually works for innova he was a former gm master tech so i hope he can figure it out im just thinking its gotta be a part not talking to each other the truck is bone stock unmolested

only other thing I can think of and I dono if it’s common for tccm to fail but the tccm that was in it was from 03 and the truck is a 2000 so I’m guessing it was changed under warranty back in the day

 

And far as putting the new encoder motor in do they usually come in the neutral position?