weird 4x4 problem 2003 Chevy Tahoe Z71

Hi!
I have something weird going on in my 2003 Chevy Tahoe Z71. The all wheel drive works better than the 4 wheel drive. If I get it stuck in 2H: (1) I switch to 4H and I am still stuck; (2) I switch to 4L and I am still stuck; (3) I switch into auto 4wd and I roll out like I am on dry ground. How can this be?


Not to long ago I changed the encoder motor because the old one died. After finding the current problem I changed the front actuator motor and the front diff oil looked terrible (including shavings on the plug) so I also put new oil in there.


When its jacked up and I let it idle in 4 hi, 3 wheels spin at the same rate with the front left spinning weakly. But on the ground the front wheels don't spin in 4hi but they do spin in auto4wd ? I don't know what to think here.



Any guidance will be much appreciated. Thanks in advance.

I find the vehicle 4wd confusing to me with your post.

your vehicle should have auto 4wd . this is activated when the vehicle PCM see a slippage.

with 4wd lo/hi you are in locked 4wd. the front axle and rear are locked as one.

when stopped and stuck you use 4wd hi/lo not auto.

when operating on slippery wet/snow roads you use auto 4wd.

with the front diff damage you may need replacement. with the encoder motor failure if that was from tranfer case fluid not replaced that could also be another repair.

the drive train fluids require replacing every 40,000miles if not used all that much . if your using it all the time hauling on dirt roads/plowing then this should be replaced every year. front/rear diff, transmission,rear diff....

operating on dry solid pavement will chew up the gears.

I find the vehicle 4wd confusing to me with your post.

your vehicle should have auto 4wd . this is activated when the vehicle PCM see a slippage.

with 4wd lo/hi you are in locked 4wd. the front axle and rear are locked as one.

when stopped and stuck you use 4wd hi/lo not auto.

I get it stuck on purpose to test the 4wd. as stated above, in 4HI the front wheels dont spin when on the ground and hence I get no traction to get out BUT when in auto 4wd the front wheels do spin and I get decent traction. I am aware that this does not make sense and that is why I am posting this question here.

Thank you for explaining to me when to use auto 4wd and 4hi and when to change the oil.

I get it stuck on purpose to test the 4wd. as stated above, in 4HI the front wheels dont spin when on the ground and hence I get no traction to get out BUT when in auto 4wd the front wheels do spin and I get decent traction. I am aware that this does not make sense and that is why I am posting this question here.

Thank you for explaining to me when to use auto 4wd and 4hi and when to change the oil.

if the 4wd does not lock in the front to rear axles then this is the encoder sticking/binding. old fluid can do this or using the wrong fluid. the tracII fluid is available at the dealer ship only last time I checked. the transfer case fluid is blue. if it is gray or worse black then change it and perhaps it will work . if not then I would expect the 4wd service light to be on if so get the GM drive train failure code and post here for some guidance.

Well it is locking. Or is it? When on the lift up in the air running in 4HI, 3 wheels spin with the front driver side spinning weakly enough to stop by hand. But on the ground the front wheels are not spinning. So maybe the center diff is unlocking under force?

I get no codes. when the encoder motor went I had c0303 and c0374. now there is no light, no code. so i cant rely on the computer to tell me what to do to fix this no traction issue.

When I looked at the fluid it didn't look awful but I will change it now just because I don't have a better idea.

Well it is locking. Or is it? When on the lift up in the air running in 4HI, 3 wheels spin with the front driver side spinning weakly enough to stop by hand. But on the ground the front wheels are not spinning. So maybe the center diff is unlocking under force?

I get no codes. when the encoder motor went I had c0303 and c0374. now there is no light, no code. so i cant rely on the computer to tell me what to do to fix this no traction issue.

When I looked at the fluid it didn't look awful but I will change it now just because I don't have a better idea.

with what your saying my guess is the encoder is working and the electrical sensors for the 4 wd are happy. the reason it is not working [traction on the front axle] is because the transfer case is in need of re-building.

normally this would be black transfer case fluid and bits of metallic material with the case drain .

you may need a front diff and a transfercase repair.

do you operate this in 4wd on solid pavement ?

use 4HI on pavement? hell no man. I changed the t-case oil and the old oil was pretty well cooked, almost black. but there was no metal on the plug. put the new oil and no luck. so ill probably have to open up the t-case and adjust something. Maybe something in there got out of whack when I changed the encoder motor? My first thought was that the t-case was blown but then how is it working for the AUTO 4WD ?

changed the fluid and no change. so tomorrow I am going to have to take the t-case apart and see whats going on in there. hopefully it just needs a little love and not a lot of money.

changed the fluid and no change. so tomorrow I am going to have to take the t-case apart and see whats going on in there. hopefully it just needs a little love and not a lot of money.

black fluid means 90% trashed.

use 4HI on pavement? hell no man. I changed the t-case oil and the old oil was pretty well cooked, almost black. but there was no metal on the plug. put the new oil and no luck. so ill probably have to open up the t-case and adjust something. Maybe something in there got out of whack when I changed the encoder motor? My first thought was that the t-case was blown but then how is it working for the AUTO 4WD ?

there are wear items in the transfer case, the black is the material that creates the friction for the axle connection front to rear. with that worn down you get this.

no codes will throw when the transfer case is worn out. these codes report the encoder/locking actuator / wiring operation.

operating in any 4wd position including auto 4wd will rapidly wear out the transfer case/ front diff. on solid dry pavement .

makes sense. but how is it that the auto4wd works if the t-case is trashed?

Very strange indeed!! Check for 12v at front actuator in 4HI, 4LO & Auto.

it looks good so im pretty sure its getting 12v. when it is jacked up the front wheel spins so im pretty sure the actuator is doing its job.

at this point I am trying to figure out weather to open the transfer case or the front diff ?? its got to the seals and gears in either one of these places. I am leaning to the t-case (even though its like an effin 8 hour job) because if the carrier in the front were broken i don't think auto4wd would work.

Front diff or t-case? any thoughts?

it looks good so im pretty sure its getting 12v. when it is jacked up the front wheel spins so im pretty sure the actuator is doing its job.

Pretty Sure? :screwy: Well, I'm pretty sure you're going to need some luck with this, so I'll start that ball rolling by saying--------------Good Luck to You.

above i already said i changed the actuator. so the chance that this is not working is slim. thanks for wishing me luck. Do you have any kind of mechanical advice?

above i already said i changed the actuator. so the chance that this is not working is slim. thanks for wishing me luck. Do you have any kind of mechanical advice?

first I would pull the front locking actuator check for damage and metal shavings.

then pull the encoder motor check for damage of the encoder and the fork etc..

when i pulled the old actuator rod was gone. all ground up and stuck to the magnet. i changed the diff oil and put in a new actuator. now the front right wheel locks. is that normal? or is the left wheel supposed to lock as well?

when i pulled the old actuator rod was gone. all ground up and stuck to the magnet. i changed the diff oil and put in a new actuator. now the front right wheel locks. is that normal? or is the left wheel supposed to lock as well?

the front axle will lock up at times some times not . sound good to me with what you have now see how it operates on the ground.

that's my issuew. when its in 4wd hi, in the air the front right wheel locks but on the ground it does not. however when in auto4wd the front right wheel does lock and give traction. thats is so wierd about this. it has occured to me that after changing the encoder motor the drive shaft when back in pretty easy. is it possible i put it in wrong?

above i already said i changed the actuator. so the chance that this is not working is slim. thanks for wishing me luck. Do you have any kind of mechanical advice?

OK, I'll hang in here for a while.

The reason I asked for a voltage check in all 3 ranges is because the front is working in AUTO but not in 4HI or 4LO. And that is your issue. You can get un-stuck in AUTO but not in the other two.

So, it's possible that the front is not getting voltage in 4HI or 4LO.

PLEASE do not reply with a "yah but" or "but why" or an "I've already said".

The reason I asked for a voltage check in all 3 ranges is because the front is working in AUTO but not in 4HI or 4LO. And that is your issue. You can get un-stuck in AUTO but not in the other two.Ok so ill check it in all three modes just to be sure but why is it that when its in 4hi on the lift the front right wheel locks with the back two? would that indicate that that actuator is good? or should the driver side wheel lock as well?

Thanks!

Follow up to this? I've got the same issue, front wheels are not powered in 4hi or 4lo but are in Auto.

Ok, I just remedied this. I pulled the encoder motor on the NP246 in our '05 Yukon and moved the splined shifter shaft around manually. The goal was to see if I could move it to any position which would power the front driveshaft, or lock both front and rear together (as 4wd should). I tested it by simply spinning the rear d/s and seeing if I could stop the front output from turning. This is easier done with a second person. In my case the vehicle was on my lift, if you do this in your driveway you'll want at least one front and one rear wheel in the air, and of course properly chock and support the vehicle. You'll have to have the trans in N or you won't be able to spin the rear d/s at all (except when you hit N in the t-case).

What I found was that I had to use pliers but all the way "forward" and all the way "back" did indeed lock both front and rear outputs together. You have to hold the shifter in these locations because apparently these auto t-cases are built to spring back out of either 4wd position, presumably to make it easier for the shifter motor to pop back out and into N or 2hi when called upon to do so.

So, my t-case WAS capable of sending power to the front d/s if the shifter was in the proper position. This meant the problem was likely the encoder motor, although I don't know if these symptoms (only able to get 4wd in "auto") mean the motor itself is weak (kind of my suspicion) or the encoder ring is failed/failing. Other possibilities included a bad TCCM (t-case control module) or bad buttons in the dash, but since all the dash button lights worked and I could hear the t-case motor move when I'd ask for 4hi or 4lo (but I wouldn't actually get power to the front d/s), I bet on the encoder motor assembly.

I should note that my initial problem included achieving low range, but I would not get 4wd low range - - and no, this was not related to the front axle actuator. This is not unusual as I've been into several t-cases and of course you have a range fork (which selects 1:1, N, or whatever your low range ratio is, in this case 2.72:1) and a 4wd fork which decides when to call upon the chain to connect front and rear ouputs as one. If the shifter is not moved fully and completely, it's possible only one of these two forks is shoved around enough, so you get half of what you were asking for such as 2lo (a desirable thing for moving around boats and trailers, but since we don't want to be bothered with locking hubs we no longer get that choice).

I should also note that I did pull codes as step 1 of troubleshooting with AE (AutoEnginuity) with full GM package, but got nothing. I also had no service 4wd light on the dash or any other indication from the truck that it thought anything was wrong. Perhaps also worthy of mention is that if my oil pump is eating thru my t-case, there's no sign of that as of yet - - of course once you see it on the outside it's too late. The pump rub issue would not explain my symptoms, but, again, still worthy of note.

I bolted on a new encoder motor assy tonight (I went with the Dorman replacement as it seems fairly well regarded and affordable at ~$160) and voila! 4wd actually works.

If I may digress a little, I feel compelled to note this is why pushbutton t-cases suck. NONE of these potential problem areas (dash buttons, TCCM, or encoder motor) exist on a manual t-case. Alas, I realize as consumers we are given fewer and fewer choices as the years progress, and indeed that pesky shifter in the floor would interfere with our monstrous center consoles. But I put 238k miles on an NP261 in our '02 Silverado and nary a wimper. It had even cooked all its fluid at some point as the 261's love to do, and I have no idea for how long it was going that way, but when I opened it up at 208k upon this discovery all looked beautiful inside. At this mark I also installed a pump rub kit but it was unnecessary, the clip was still in place although it was showing signs of wear. I refilled with 5W-30 (do NOT do this with the autotrac NP246) and we finally sold the vehicle at 238k miles.

Follow up to this? I've got the same issue, front wheels are not powered in 4hi or 4lo but are in Auto.

this member has a damaged front diff and a transfer case that is blown. much different than your problem . he replaced these encoder/actuators and still no fix because these 4wd diff/transfer case are trashed. checking the drive train fluids for level and condition will make this a reliable 4wd system. replacing these fluids is also required at 40K miles . push buttons are a better system the only problem is/was would be the wires used to the transfer case from the controller/fuse as they are fragile.. this means if a tech does not properly handle these you will have failures .. tooo many have had this occur on these forums ..damaged wiring due to poor work .