4WD wobble followed by service 4wd light

[AbleDanger]

Love the site and you have all helped me do so many things to my 2002 Trailblazer heirloom (Grandfather bought it new, then on to dad, me and now my kids). I have searched and searched for some answers and cannot seem to find anything that is close to what I am experiencing.

Here is the deal.... I did a tremendous amount of work over the last 24 months as I have been trying to get this old girl sorted out for my kids to drive. I have done a ton of work but I have had this wobble that only happens when I am in 4wd. The wobble is basically a small back and forth shake in the steering (like 1/2 an inch either way) and the frequency increases and decrees with speed. It is important to note that this only happens when the 4wd is engaged. So in 4hi or 4lo it is doing this all the time. In 4awd mode (or whatever that is called) it only does this as the front is engaged.

Now, I didn't really care much because the kids only really drive it back and forth to school. It gets about 5k in miles a year at best. And they don't really drive too much in the snow so I thought I could live with it.

Today, the 4wd service light came on. My daughter had it in 4awd overnight (it snowed here) and when the light came on it shifted to 4hi (4awd was selected) and the switch was flashing. It has done this before and you just shut the truck off and it goes away, but not this time. So when I went to pick up the truck, 2wd was selected but the truck had a solid light over 4lo. When I plugged in the code reader, nothing came up. The truck was not on but it then decided to shift back into 2wd and the truck rolled (it was still off).

I drove it home in 2wd with no issue. When I got back to the driveway I tried to see if I could shift it to 4awd and hear anything. I heard the shift but the service 4wd came back on and it jumped to 4hi this time flashing.

I am about to start the process of diagnosing the disconnect but let me first tell you what I have done in the last 24 months to this thing...

1. Wheel hubs replaced - both sides, not sure brand but rock auto middle-priced something or other. One might be bad as I am also getting a slight vibration.
2. upper and lower control arms - new
3. CV joints - Replaced them both, and even replaced one again. Both are Surtrack as I had issues with other brands
4. new Bilstein struts
5. Outer Tie Rods
6. Moog end Links - One is bad as I put 2.5" blocks to lift the front
7. Diff fluid and TC fluid changed (used the smurf blood in the TC).

I have a 2.5" lift on the front and have flipped the control arms. All the bushings and ball joints are new in the last 12 months. Alignment was in the spring with new tires.

I suspect it might be the disconnect as that is about the only thing I didn't dig into when rebuilding the front. However, the light jumping around seems odd and thought I would ask before I got too deep into this because it is COLD out!.

Thanks

 

[TollKeeper]

There are write ups on the forums, but I would start by doing 3 things.

WIth the key on, and engine off, switch it into A4WD, you should hear 1 motor engage
With the key on, and engine off, switch it into 4WD, you should hear 1 motor engage
How you respond to us about those sounds will help in telling you where to start.

Also, with the front right wheel off, check where the CV Axle goes into the oil pan/Disconnect, grab it firmly with both hands and move it up and down, side to side. There should only be a minimal amount of play. If the bearings are gone, this could cause the steering wheel shake, and ultimately, a possible disconnect failure.

 

[Mooseman]

That wobble is called "crow hopping" and is normal with 4x4 engaged on a high traction surface like asphalt. That's why you wouldn't use it in these situations.

The Drivetrain FAQ sticky at the top of this section has this to help you:
4WD not working? Step inside.

 

[AbleDanger]

Thanks for the replies. Sounds are present when in A4WD and 4HI. The 4Hi is a bit weaker sound but it is present. I will have to wait for a garage to get to test the CV Axle. Its a cold night in Cleveland.

Mooseman, I am familiar with Crow Hopping as I have had many 4WD. This is actually present when going in a straight line and is the same no matter what the position of the steering wheel. In fact it's much more subtle than the crow hopping sensation, it feels like one of the tires is out of round. I thought it was a bad CV axle but I have swapped out 4 (2 on each side plus the originals) and it makes no difference and even thought it was an old tire perhaps, but it stayed when I replaced the tires entirely with a fresh set. It is most noticeable under power but is still felt when coasting.

I will let you all know when I test the CV axle at the disconnect. I suspect that might be an issue. Can't wait to get that separated from the oil pan!

 

[TJBaker57]

With regards to the selector switch being in one position and the transfer case and/or switch position light in another....in addition to the links already provided here are a couple more.

4WD Selector Switch

After many years of cycling the 4WD selector switch it got to the point of not resolving itself. After observing the voltages (fluctuating) with the Tech 2 I ordered a replacement switch but in the meantime I disassembled the original switch, cleaned the contact surfaces and it then worked fine...

gmtnation.com

DTC C0327 Resolved

So after many years of occasional issues with the transfer case shift motor encoder I decide to fix the damn thing. Hooked up the Tech 2 to display the encoder return voltage and take it under the truck with me. Wiggle this, push pull that, tap here and there all the while watching that return...

gmtnation.com

One shows the selector switch disassembled for cleaning (I never did install the new one I bought) and the second shows the innards of the transfer case shift motor (encoder motor), specifically the encoder ring that when working correctly reports the shift motor position to the TCCM.

A couple things worth noting. The selector switch does not control the indicator lights that display on the switch. The TCCM does that. Both the selector switch and the encoder/motor send varying voltages to the TCCM to either request or report a particular mode of operation. If you're anywhere near my age (doubt that) you would remember old radios or televisions and such with volume knobs that got old and dirty and would make scratchy sounds in the audio when they were adjusted. Similarly the selector switch and encoder ring can get schmutz in their workings and then not send a steady signal back to the TCCM. Without a clean steady signal the TCCM will frequently decide a shift has failed and is supposed to go back where it started the shift from I think. With a dirty or failed encoder ring the TCCM will not even know where the shift motor (encoder) is presently.

 

[Mooseman]

Mooseman, I am familiar with Crow Hopping as I have had many 4WD. This is actually present when going in a straight line and is the same no matter what the position of the steering wheel. In fact it's much more subtle than the crow hopping sensation, it feels like one of the tires is out of round. I thought it was a bad CV axle but I have swapped out 4 (2 on each side plus the originals) and it makes no difference and even thought it was an old tire perhaps, but it stayed when I replaced the tires entirely with a fresh set. It is most noticeable under power but is still felt when coasting.

Ah, sounded like you were describing crow hop or some version of it. I was also thinking it may have been a difference between front and rear tires but you replaced them. Could be a worn bearing in the disconnect allowing the axle to wobble. Maybe check the driveshaft for a bad U-joint. Hopefully it's not something more serious like the diff or transfer case.

 

[AbleDanger]

Some updates.....

Today the service 4wd light is gone and it is shifting between everything correctly. I didn't run it long or far, just pulled it into the garage. I did notice that the disconnect motor noise was much longer and louder than yesterday. Perhaps that could be one of my issues.

I first put it in 4hi and lifted the right side (honestly I first lifted the other right side but i realized my mistake)... with the right front wheel in the air it will not turn with the left on the ground. So disconnect if functioning.

I then grabbed the right CV axle at the disconnect and moved front to back and side to side.... it has play but I am not clear on how much it should have. It is enough to make some noise but not more than a millimeter or 3. Can anyone clarify the amount of play it should have?

Also back in 2008 before I had the truck, my dad replaced the TCCM. It got the 4wd working again so I didn't think of it until now. I have no records or what he replaced it with, I believe it was a GM part but I don't know if it was from a 2003 or new, etc. I will ask him but health may prevent him from remembering. May not be related but worth mentioning.

I plan to try and clean out the switch as the TJBaker57 linked to earlier. That makes a ton of sense and I did see that post earlier but never thought it could be related. Thanks

 

[HARDTRAILZ]

What lift kit? Did it bolt on top of the strut?

 

[TJBaker57]

Can anyone clarify the amount of play it should have?

This was mine in 2014....too much play!!

New video by Thomas J Baker

photos.app.goo.gl

 

[AbleDanger]

Hardtrailz - not sure the brand but it is the bolt to the top of the strut. Did it when I did all the other suspension work. I also replaced the strut mounts when I did that. The only thing that came from the factory up there is the springs, steering knuckles, and calipers.

TJBaker57 - great video. I have about half that in interestingly it is on both sides. I guess that would be true since the intermediate shaft sits on that same bearing, correct? I am thinking it still may be too much. I think I will get it apart as soon as I can and at least replace the bearings. I just hate to do all that work and find out it was not the issue.

 

[HARDTRAILZ]

The lift is causing binding. Those style are referred to as death lifts on these. The lengthening of the strut assembly cause serious and dangerous issues. Binding, breaking splined disco, ball joints popping and removing the entire tire and wheel while driving are all problems found with these style lifts.

Could also be the splined disco is busted from the lift and creating the wobble. take a look at it for sure as well.

 

[AbleDanger]

Hardtrailz, I think I may be describing the lift wrong. It was similar (really identical) to the BDS front lift and it was actually only 2.0". I had seen some of the problems you mentioned when exceeding 3" but will be researching the issues you bring up. Wheels and tires falling off! Holy crap that is very serious and surprising for only a 2" difference in altitude.

However, this wobble (and these issues) preceded all of these modifications. Again, I thought it was a bad tire and so I did all the modifications first and changed the tires once I had the set up together the way I wanted it. I still am going to check on the disconnect as I cannot think of that wobble being anything having to do with the current suspension set up since it was exactly the same prior to all the upgrades but who knows. I had thought it might be a ujoint as suggested earlier but I am getting to the point that the truck is gonna rust out before I get to the bottom of this. It was supposed to be a fun project for me and my kids lol

 

[HARDTRAILZ]

. I also replaced the strut mounts when I did that.

Hardtrailz, I think I may be describing the lift wrong. It was similar (really identical) to the BDS front lift and it was actually only 2.0". I had seen some of the problems you mentioned when exceeding 3" but will be researching the issues you bring up. Wheels and tires falling off! Holy crap that is very serious and surprising for only a 2" difference in altitude.

You can't have the new mounts and the BDS style lift. The BDS replaces the mount you claim is new.

2 is not the issue. It is 2 via strut extention by a kit that goes on top. You can safely do 3 provided the lift is inside the strut for the bulk of lift and maybe 1/2 inch outside strut. You put 15/2/3 or anything really outside of the strut and you get issues.

Tires fall off when the ball joint fails going down the road. Pictures come up on FB and its almost always the cheap slap on top lifts that cause it.

 

[AbleDanger]

Gotcha. Found the name. They are Rough Country. So the strut bolts in on the top of the block but it sits on top of the spring. I replaced whatever I could outside of the springs that didn't come with the kit. Sorry that was two years ago and have done a ton since then to the truck (not just suspension) so my memory is a bit foggy. I also did some work to a few other cars with at the same time.

Ball joints have over 10k on them and are solid as the day I put them in. No grease leaks and super stiff. Had it apart a few weeks ago to get at the header I needed to remove. But I do get that lifting this thing in any way will cause load on that bearing so I think I will tearing into that as soon as I can. I will update when I am able.

 

[HARDTRAILZ]

Rough Country is not a death lift. Check the bushing on it though. Some had those fail and it could be contributing to your issues.

 

[AbleDanger]

I will, thanks. I might just replace it to be sure.

 

[TJBaker57]

have about half that in interestingly it is on both sides. I guess that would be true since the intermediate shaft sits on that same bearing, correct?

No. All the play in my video is the output side of the disconnect. The intermediate shaft has its own bearing on the input side.

I dropped the shaft along with the disconnect as it didn't want to separate, perhaps due to the damage inside the disconnect.

 

[AbleDanger]

TJBaker57 - I like the watch laying next to the parts. A nice touch. I can't tell you how many times I can't find my watch on Monday after spending a weekend in the garage!

I appreciate the picture. In pricing out parts I see that the disconnect actually has 3 bearings inside it. So perhaps mine is in spec and something else is to blame.

 

[AbleDanger]

Sorry for the delay.... here is the update. Dug into suspension and Hardtrailz was correct, bad bushing seemed to have things off a bit. Also, the CV axle on the left came apart. I cleaned it and greased it and put it back together since it was only a few months old. Wobble seems to be almost gone. Might be that CV axle but I will get after that when the weather breaks.

Now, the 4wd issue seems to be completely separate. In fact, I had a new service 4WD light come on. My cheap reader registered no check engine light but the lights on the switch disappeared completely. Then a day later they are back working fine. It has done this once or twice in the past, but the frequency is increasing. I plan to replace the switch and check power to the appropriate fuses to rule out everything I can. I don't have access to a Tech II.

Also, I have already run through the 4wd diagnosis checklist. Jacked up the front right wheel in 4hi and the wheel does not move. I also hear both motors kicking over so transfer case motor and disconnect motor seem to be functioning correctly. I am hoping it is something simple but seems it might be the TCCM. Any other culprits to be aware of? I have read through everything and it seems that might be the answer here if not the switch or a bad wire. My dad replaced that 5 years ago but might have replaced it with a 2002 unit, not sure.

Thanks again for at least solving one of my problems. I appreciate the help.

 

[droptopgsx]

A general code reader only reads ODB2 or possibly abs codes, to see the tccm codes you need a tech 2 or equivalent scan tool. Without knowing what the code is or seeing the data that the tccm is seeing it's at best an educated guess to say for sure what it is. Tccm failures are pretty rare and the Encoder motor is very common failure, but it could be a ton of things. The encoder motor is probably 100-250+ bucks depending on if you trust dorman or remanned parts vs OEM new so it's not a cheap 'parts cannon' thing to do but 95% of the time it's either the disconnect, the switch, or the encoder motor.

You could, I guess if you wanted, probe the inputs to the tccm directly and see if the inputs are doing what they are supposed to be doing. The tccm putts the control for the front axle out on the blue wire, and watches the black/white wire for confirmation that it is in the mode it should be. So if you put a volt meter on it you should see it switch between 0v and 12v depending on whether you are in 2wd or a 4wd mode.

The selector switch signal wire is the light blue wire and it is a 5v wire pulled to ground through varying resistors so if you want to test it you could unplug it from the tccm and measure resistance between the gray wire and the light blue wires. 2wd position is 240 ohm, auto-4wd is 560 ohm, 4hi is 1100 ohm, 4lo 2200 ohm, neutral 5100 ohm. I don't know what the value of the pull-down resistor is inside the tccm to be able to say what the voltages would be with it plugged in but whatever they are it should be fairly steady and bumping/fiddling with the switch should not show any huge jumps in resistance (unplugged) or voltage(connected to tccm).

The encoder motor is basically a tps sensor/potentiometer/variable resistor for the position of the motor. Should vary from .5v to 4.5v depending on where the motor is. If you wanted to you could monitor the voltage on the brown/white wire and switch it between modes, it should change voltage smoothly and not have any dropouts or anything.

 

[AbleDanger]

droptopgsx - Thanks for the info. As I said I hear the motors working and the front right tire does not spin when it is (solely) up in the air with 4hi engaged. We replaced the switch last night and this morning (was really cold btw) it decided to just switch itself info 4lo.

I will see if I can get access to a good reader and see if I cannot pinpoint what the heck is going on.

 

[Matt]

Since you're throwing parts at it, try and source an 03+ TCCM. If your Dad replaced it once already with an 02 then that may very well be the culprit as the 02's were flaky.

 

[Mooseman]

and get an 03+

 

[AbleDanger]

All I seem to do lately is throw parts at this thing. I am running out of parts to replace.

 

[TJBaker57]

A general code reader only reads ODB2 or possibly abs codes, to see the tccm codes you need a tech 2 or equivalent scan tool.

Actually, I read and reset TCCM (node 1A), EBCM (node 29), BCM (node 40) and all manner of other module codes fairly frequently with my $15 chinese clones of the ELM327. I will not say it is easy to learn,,, unless you are one of those command line geeks . Additionally I only know this to work on the older vehicles that are pre CAN Bus, J1850 VPW.... Like this current thread is dealing with. I have used hyperterminal and an old Windows XP netbook but I more frequently use my android and an app called serial bluetooth terminal by Kai Morich. The biggest frustration for me is androids inability to maintain the bluetooth connection! Fortunately it is a single button press in the app to reconnect. Also, this is a hands-on terminal operation. There is no software that does the work for you, you need to learn how to talk to the network yourself.

How To Guide: Reading TCCM Codes

Last year I spent a lot of time trying to pull TCCM codes from an 02 trailblazer. At the end I was able to access them manually via the command line. Below is the writeup on it. Hopefully this helps some folks diagnose their own 4WD issues :) There is a lot of info below, if you are looking...

gmtnation.com

 

[TJBaker57]

Also useful for reading TCCM and other codes is the Android App "Car Gauge Pro". Its' operation is a little quirky but it is very useful once you get it figured out. NOT for use with CAN Bus (GMLan) vehicles. I have used it with 2002 and 2004 4.2 engines, TrailBlazer and Envoy, and my 2005 5.3 LM7 Yukon.

 

[AbleDanger]

Thanks, TJBaker57. I have a Bluetooth ELM327 on the way now as I had seen this option on previous posts. I actually already had one delivered this weekend because I have a 2002 but it was a wifi version and I could not get the damn thing to work with any of the apps. Hopefully, the Bluetooth version works better.

 

[TJBaker57]

And I have wondered if a wifi version would work better!! With Torque and Car Gauge Pro I have no issue with the Bluetooth adapters but when using a terminal app I frequently drop the connection. Either from inactivity or maybe a buffer overrun.

 

[Mooseman]

I find the wifi works a bit better with my Android HU except with the one I have, I have to unplug it or it won't reconnect. I think it's because of interference from other bluetooth devices or connections.

 

[AbleDanger]

I found the Bluetooth worked better but that might be because I went for a better quality version so I would default to Mooseman. Now the codes are not showing up and things are working great. I think it may be due to temperature. It is in the high 50's F this week so I will have to wait for freezing again to see some codes. None were stored for the scanner to see. She is fighting very hard!

 

[AbleDanger]

So the temp dropped but everything seems to be working. I pulled a code of P0327. @TJBaker57 I see your post on replacing the transfer case/encoder motor. In that posting your title references the same code. Was that the reason for you replacing the encoder?

 

[TJBaker57]

So the temp dropped but everything seems to be working. I pulled a code of P0327. @TJBaker57 I see your post on replacing the transfer case/encoder motor. In that posting your title references the same cod

Confirm your code for me...P0327 as stated or C0327? Different codes there.

I replaced my encoder ring, NOT the whole motor, because testing revealed it to be bad of course the sensor alone is of course cheaper than the full unit, but if the sensor alone is not the issue then you have to shell out more for a complete unit. So thorough testing is essential.

Symptoms were that I could hear the motor shift, sometimes successfully and sometimes not. Sometimes the selector light would blink as it should while performing the shift but the shift would seemingly fail and the light would return to the previous setting. I had studied the system operation through various web resources and had my suspicions. I then acquired a Tech 2 that allowed me to see the sensor return voltages from the encoder sensor. The instability of the readings in certain modes confirmed the sensor was failing. One could conceivably test this out with a DMM and backprobing the connection of the return voltage of the encoder/motor at the TCCM.

Is your service 4wd light on now?

 

[TJBaker57]

pulled a code of P0327. @TJBaker57 I see your post on replacing the transfer case/encoder motor

Another question: assuming this is actually C0327....what did you pull the code with? What software? And is it a current code, a pending code, a history code, or maybe an old or Intermittent code?

 

[AbleDanger]

@TJBaker57 The code was C0327 pulled with an ELM327 Bluetooth using an android with Car Gauge Pro (I paid for the app). It was a history code. No current codes at all. I cannot get the thing to throw a service 4wd again. It only does it when I am not driving it or when I am not around. See the picture for details... I had some other stored codes as well. I assume they are not related.

 

[AbleDanger]

@TJBaker57 I ran the truck briefly with fuse 8 pulled so I assume that is U1026. Also, my symptoms sound similar to yours except that it seems to jump to a setting I didn't ask it to (for example it was in 2Hi setting and jumped to 4Lo setting when the kids backed it out of the driveway.

I also did some meter testing per @droptopgsx suggested at the TCCM and things were fine while moving everything back and forth.... then when I was done it threw a service 4wd light (didn't have the reader yet).

 

[TJBaker57]

So....history code. That means it has happened previously but isn't currently happening. History codes remain generally for a given number of 'drive cycles' or the like where the error is not seen. Might be a number as high as 100. In my experience this error doesn't just go away on its own. Environmental conditions do seem to play a part.

 

[TJBaker57]

My 02 also once switched to 4lo, might have been 4hi, on its own as I was turning into a parking lot at low speed. Felt like all tires went flat!! I have wondered if the tccm, getting erroneous feedback from the encoder ring might drive the shift motor incorrectly.

 

[AbleDanger]

My 02 also once switched to 4lo, might have been 4hi, on its own as I was turning into a parking lot at low speed. Felt like all tires went flat!! I have wondered if the tccm, getting erroneous feedback from the encoder ring might drive the shift motor incorrectly.

Based on your write ups and what I have seen elsewhere on this site I think this might be the situation. I also mildly suspect that my motor might be weak. Gonna test the wiring one more time to rule that out and might just get the whole motor assembly to be sure. Thanks for the help!