So I have read (nearly) every post about the woes of 98 blazer 4wd problems and have an additional question. Last fall, my blazer was following the same pattern others have reported of 2 HI, 4 LO only (when in neutral), blinking 4 HI & 4 LO lights before going back to 2 HI when pushing the 4 HI button (also in N, nothing when moving). I was pretty sure the problem was related to a bad encoder motor, so I ordered a remanufactured motor and installed it. No problems all winter. Just the other day, I bumped the switch when putting the blazer into gear and, after a loud "clunk" and dropping into 4 LO, it's back to 2 HI / 4 LO only.

So here's my question: is this just a bad motor or is something else the culprit? Perhaps something putting extra strain on the motor and burning it out?

Any thoughts for a systematic troubleshooting plan would be appreciated.

Thanks!

 

I just redid the 4x4 system (front axle and t/c system) in our '96. Mine never did what you describe. Mine started randomly blowing fuses when I'd push 4hi. I pulled the encoder motor and removed the plastic cover on the electric motor. If you've ever been around electronics and smelled a shorting or burned out component you won't forget it. Got a replacement at the jy and all is good. So if your not blowing fuses I'd guess the motor isn't burned out. I've been told that it's possible that the TCCM can get stuck in a mode that sends the wrong signal/signals to the encoder motor. Although this wasn't my problem I was told to disconnect the negative terminal on the battery for at least 30mins to reset it. Can't hurt to try.

 

My first suggestion is to remove the 4wd switch assembly, separate the two halves to access the PC board and then re-flow all the solder joints. Be careful separating the halves due to plastic tabs.

I think this can be done:
remove encoder motor from t-case
use a wrench to check that the t-case can be switched - put back to original position.
start engine and with encoder motor off the t-case, have another press the 4HI, 4LO, 2HI buttons while watching the encoder motor movement. Just be sure to put everything back into the same mode before re-installing encoder motor.

Now this is where my diagnostics ends - if the encoder motor does not move correctly it could either be the motor or the TCCM. I do not know how to further isolate at this point, perhaps another will be able to continue from here.

 

I decided to recheck the vacuum actuator under the battery. It seems fine (at least the rubber seal around is intact), but it sounds like I can hear air escaping from somewhere when I manually squeeze the actuator. Of course the vacuum line is in a plastic shield and then disappears quickly back toward the fire wall. Does this sound like a vacuum leak? Should I be able to hear what sounds like air escaping when I squeeze the actuator?

Thanks for your help so far!

 

You can remove your battery and the shelf it sits on (two 13 mm bolts you reach in the front of the wheel well) to see it. Then use jumper cables to start the truck or lay the battery in there to start it. You can remove the the battery while the truck is running.

I was sorely temped to move mine out from under there when I checked it.

Another way to check it is to find the cable with your hand and hold onto it and have someone start the truck and activate the switch. This is a little scary because the fan belt is just to the right of your arm while it's running. It is less stressful to find the cable when the truck isn't running. You can feel the movement in the cable when it moves.

 

Also, I got a DTC code of 2, reset the TCCM with a battery pull, no codes at first. After the reset, everything seemed to be fine for a few 2 HI - 4 HI cycles then back to the old 2 HI - 4 LO only and now has the DTC code of 2. I'm assuming based on what I've read that this is the encoder motor, but since I just replaced it in September 2013 I don't want to miss something else.

Thanks again!

 

Do you think your front axle was engaged after the battery pull and while 2hi/4hi was working? Best way to check your front axle engagement system is with the vehicle running. To make things simple I cut the center out of the battery tray. The air you hear when squeezing the actuator could be a leak or it could be air exiting the vent tube. Actuator couldn't deflate without that vent. The vaccuum switch on your transfer case has three hoses. One is a vent tieing into a tee near the t/c,one goes to the actuator,and one to a junction at the vaccumm reservoir. One thing I found out is that it doesn't take much of a vaccuum loss for this system not to work. Of course this wouldn't be the cause of your 2hi/4lo problem.

I did what LennyL81 did with the switch. But after handling a new one in comparison to mine I found my buttons to be not so positive when pushed so I replaced it. Much brighter lights to. I got my replacement encoder motor at the jy I deal at($65 and if it doesn't work we'll keep trying until we find one that will). First one worked. Rather than doing it the way LennyL81 describes,which is fine,I took the motor apart to clean and regrease it then pulled the t/c engage gear and put it in the right position so the motor would mount properly. Fired the vehicle up and all is good. For what it's worth,that friend who runs the jy told me that 9 times out of 10 t/c mode problems are caused by that motor. At least in my case he was right. Sounds like yours,although not burned out,may not be working right. Still under warranty?

 

Thanks EZEARL. The motor is in fact still under warranty, and the replacement arrived yesterday. I'm loathe to replace it, though, if something else is causing the malfunction.

I think you're right about the vacuum vent. That's exactly what it sounds like, but I wasn't sure whether there was a vent so when I heard air escaping I immediately thought it might be a leak.

After again resetting the stored code in the TCCM, everything seems to work (for awhile). I took it for a test drive and was able to shift in and out of 4 HI without a problem. The only remaining problem seems to be a random malfunction when going into 4 LO, successfully I might add. Sometimes after switching to 4 LO then back to 2 HI (or 4 HI), things revert back to only having 2 HI and 4 LO--until I pull the courtesy light fuse again (#8 in the inside fuse panel I think) for a couple of minutes and resetting the TCCM code with the 5 on-off cycle process.

For now, I think I'll just leave it well enough alone unless I can think of something else that might be causing the problem. Given that the encoder motor seems to work fine after a reset (and I checked that 4 HI was engaged by trying to move the front drive shaft by hand--it won't move when in 4 HI, but will in 2 HI so everything seems to be working), I'm still not convinced that it's not something with my TCCM. One would think, though, that I would get a DTC code related to the TCCM if that were the case. A real head scratcher!

Thanks again. Any additional thoughts anyone might have will be greatly appreciated!

 

GLAD to help out and I hope your problem's solved.

Here's some interesting info. My son stopped and talked to our friend at the jy about a TCCM for a buddy with a '96 Blazer(turned out to be his encoder though). He was told that the TCCM was protected from electrical damage in some way. Yours is different than mine so.....
If you would come to trying another TCCM maybe try the jy. Our jy charges $65. Same as an encoder with the same "return til you get a good one" deal. Although my problem was blown fuses,and not a mode problem,after a battery reconnect my system worked fine. But eventually it would blow the fuse and was doing it more frequently. Good TCCM,bad encoder.

 

js, you are having the same problems I am having. My Blazer will go 2Hi to 4Lo only. I read on the forum it is either the tccm or encoder motor. I had different encoder motors and all worked for a day and then started acting up. All were used. I threw out the vacuum problem since it will go into 4 lo. I had everything checked by professionals and they said that do due to the vehicles age they could not scan it properly. WTF. I recently found some new mechanics and am going to ask them about this. As long as I have 4lo I am content for now.