4WD MALFUNCTION

[de3jr88]

Greetings all. Was time for an oil change on my '03 Envoy 4.2. I have always had trouble getting on my ramps in 2wd so I tried shifting to 4wd. I heard the actuators run but the 4WD light on the selector kept flashing. Turned the selector back to 2wd, heard the actuators again, 2wd light is solid. Tried 4WD again, same thing but now the 'Service 4WD' indicator comes on the dash. Back to 2wd again, shut engine off, restart and service indicator gone. 2wd light is on. I took it for a quick loop in front of the house to make sure nothing is hung up and all seems normal in 2wd.

We rerely use the 4WD on this vehicle. In the 12 years we have had it, we have maybe used it 10 times. Regular maintenance has been performed, there is 230000 kilometers on it.

The 1 time I used it last winter, it took a couple of tries to get 4WD to work but I never noticed the light flashing.

I just tried engaging it again. Tried with just the key 'on' but engine not running. Turn to 4HI and I hear the high pitch whine of the diff actuator, but not the second lower pitch noise from the transfer case. 4WD light is flashing, turn back to 2wd and it is solid on 2wd. From reading other threads, this tells me that it is likely the TC encoder motor.

Anyone have any other suggestions or thoughts?

 

[Mooseman]

This thread from the FAQ has good troubleshooting steps to follow:
http://gmtnation.com/forums/threads/4wd-not-working-step-inside.106/

 

[Wooluf1952]

Just a suggestion; When you get the transfer case to change, use 4LO. The truck will almost walk up the ramps without giving it any gas.

 

[Matt]

I'm calling it early, your disconnect is toast. Easy way to tell. Get under the truck and grab hold of the axle on the passengers side right next to the diff and start wobbling it around, it should barely move. If it does move a lot, your disconnect is done.

 

[de3jr88]

This thread from the FAQ has good troubleshooting steps to follow:
http://gmtnation.com/forums/threads/4wd-not-working-step-inside.106/

Thanks! I have read thru it and have a couple more things to check tomorrow. I am hoping that it confirms what I know so far and doesn't raise moe question. Really appreciate th

I'm calling it early, your disconnect is toast. Easy way to tell. Get under the truck and grab hold of the axle on the passengers side right next to the diff and start wobbling it around, it should barely move. If it does move a lot, your disconnect is done.

Thanks for the reply Matt. Due to the snow storm here today, not gonna be able to do that until tomorrow. Are you thinking the disconnect is toast as well as the TC encoder? I have power and noise from the disconnect but nothing from the TC. I will do more investigation tomorrow when the storm has passed.

 

[Matt]

If there's movement then it's the disco, probably a broken fork. Mine was buggered, I believe the TC was fine but I replaced it as a whole unit using this: http://www.ebay.com/itm/Trailblazer...bly-/161509934124?vxp=mtr&hash=item259abe042c

If you just need the disco then you can get this one: http://www.ebay.com/itm/Trailblazer...NEW-/161631760954?vxp=mtr&hash=item25a200f23a
Hopefully you won't have a problem getting it out like I did. I broke the housing (close to 80% of them break trying to get them out because of corrosion) This is what you don't want:

 

[Mooseman]

And if you do get it out intact, clean the hole and disco and apply some anti-seize liberally.

 

[de3jr88]

Sorry I've been inactive on this. Between the weather and busy work sched just haven't had time to do further investigation. Tuesday should be a good day to try and finish the diagnosis. i will update then. Thanks.

 

[de3jr88]

So today I did more investigation. Had a buddy with me so I could be underneath while turned my switch from 2hi to 4hi.

The noise I hear is coming from the TC encoder. I was sure is was from the front disconnect, but I was wrong. 4HI light is blinking non-stop. I put my hand on the TC motor while having the switch turned and can feel it doing its job. Moved to the front diff on passenger side, had the switch turned again and theres nothing. I can feel it click when the switch is turned back to 2HI. The CV shaft does not wobble around.

Jacked the right front off the ground, turned the switch again. Right front wheel turns freely so obviously the front diff is not engaged. Lifted both front wheels off the ground, turned the switch to 4HI, spun the LF wheel and it turns by itself, prop shaft does not turn.

But while I am turning the LF wheel (switch still on 4HI light blinking), the disconnect motor suddenly engages and the front wheels spin opposite of each other. I repeated this again and it did the same thing, it will only engage if the front wheels are turning.

So, I took it onto the street and rolled along slowly and turned the switch to 4HI and it engaged right away as it should. Turned back to 2HI and it disengaged right away.

Clearly the front disconnect has an issue. Is this something I should just run until it completely fails or should I just replace it and be done?

 

[Mooseman]

I'd be taking it apart. It could just be it needs freshening up with a good cleaning and regreasing. This article has good detail on the innards and how to rebuild it.
http://www.offroadtb.com/articles/tech-docs/front-axle-4wd-disconnect/

 

[medicmandan]

Any updates? I had this same issue surface this morning. I wasn't able to play with it much but I can definitely hear the axle actuator whirring while I try to switch from 2HI to A4WD. Not sure if I am hearing the encoder motor kicking in. I will have to crawl under it tonight.

 

[Mooseman]

Welcome. Did you check this thread?
4WD not working? Step inside.

 

[medicmandan]

Welcome. Did you check this thread?
4WD not working? Step inside.

I was planning to tonight but when I got home it was all working. No issue going back and forth between all modes.

Only strange thing was after turning it back on the N light came on and the 2HI was flashing. I shifted to neutral and it went solid on 2HI. Seems there is still some kind of a problem.

 

[Mooseman]

Could be the encoder motor not able to shift through all the modes.

 

[medicmandan]

Could be the encoder motor not able to shift through all the modes.

Seems to be working fine now but who knows for how long. Would hate to spend $200 if I couldn't isolate it to that but I really don't want it to die on me either.

 

[Spenceryaden]

I know this is a late reply but I stumbled across this and wanted to give some input. I had a similar problem where the 4wd hi and low lights would flash and only go back into 2wd. The "service 4wd" light would come on the dash. I heard everything clicking and engaging underneath but I couldn't get it to work. As a last resort before throwing money at it, I found the 2 ground wires on the frame (driver's side) of my 04 Silverado and noticed the undercoating was gunked up around them. I took them off, cleaned them and reattached. I haven't had an issue since. Maybe look for grounds underneath near the transfer case and inspect their condition.