Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

1 - 20 of 76 Posts

·
Banned
chevy
Joined
·
1,091 Posts
:) Please read me before making a post. :)

There seems to be quite a lot of mystery to newer folks when their 4x4 functions stop working. Since crappy weather season is upon us a lot of people are trying their 4WD functions for the first time this year... and discovering all isn't as it should be.

Here's my attempt at a troubleshooting checklist/flowchart. Hopefully this helps folks get a handle on what's wrong with their setup and how to fix it.

Information in this thread applies to 360/370 trucks with selectable 4WD functions (TrailBlazers, Envoys, Ascenders?). Trucks with non-selectable AWD (Rainiers, 9-7s, Bravadas) may find some of the information here useful. However AWD trucks lack some of the parts discussed here.

On to the show.


Gah! My 4WD doesn't work! What do I do?

Is the Service 4WD light on?

Yes: Go to Section 1.

No: Go to Section 2.



Section 1: My Service 4WD light is on.


Are there any lights lit on the 4x4 selector switch?

Yes: Go to Section 2.

No: Try these steps.


  1. With the ignition off, rotate the 4x4 selector switch from left (2HI) to right (4LO) and back again about 20-30 times. With lack of use, the contacts inside the 4x4 selector switch can get a light amount of oxidation on them. Repeatedly rotating the switch can sometimes clear this problem up. If this doesn't help, read step 2. If step 2 doesn't work for you, replace your 4x4 selector switch. If replacing the 4x4 selector switch doesn't work for you, try to find a local member with a verified working TCCM to swap in. If the problem goes away, return your friend's TCCM and buy a replacement for yourself. Search these forums for replacement instructions.

  2. On some 2002 model year trucks, the Transfer Case Control Module (TCCM) can have trouble waking up when the engine computer tries to talk to it. Fuse #8 in the engine bay fuse block provides power to the TCCM. Pulling this fuse and replacing it will usually wake the TCCM up and allow the use of 4WD for a time. Fixing this requires either a dealer software update (can be spendy, doesn't always work) or replacing the TCCM with a unit from a 2003 or newer model with selectable 4WD.


Section 2: Checking the motors.

With the ignition on, switch the
4x4 selector switch from 2HI to 4HI. You should hear two distinct mechanical whirring sounds. One from the middle of the truck (under you) and one from the front of the truck.

I hear both whirring sounds:
Go to Section 3.

I don't hear the sound from under me: There is an issue with the Transfer Case Encoder Motor. Check the connector going to the motor(cylinder looking thing) on the transfer case for damage/corrosion. The motor may require replacement.

I don't hear the sound from the front: There is an issue with the Front Axle Disconnect Actuator. It is plugged into the Front Axle Disconnect (AKA Splined Disconnect) located under the truck on the right side of the oil pan. Check the connector attached to it for damage/corrosion. If the connector is OK, replace the actuator.


Section 3: Identifying mechanical failures.

Turn the ignition on but don't start the truck. Place the
4x4 selector switch in 4HI. Using a jack/jackstand raise the LEFT FRONT wheel off the ground. Try to turn that wheel by hand.

The wheel does not turn freely:
If you've followed the troubleshooting guide without skipping ahead and come this far, then you have an issue that is beyond the scope of this post. Possibilities are an intermittent problem in the
Front Axle Disconnect, front differential failure or transfer case failure. I recommend you make a post in the 4x4 section detailing each of the steps in this guide you just followed. Also note any noises you may be hearing while driving in and out of 4WD.

The wheel turns freely:



  1. Crawl under the truck so that you can see the front driveshaft. Have an assistant turn the left front wheel by hand. Can you see the driveshaft turn? If so, you have an internal transfer case failure. Most likely due to worn out clutches. If not, proceed to step 2.

  2. It is likely your Front Axle Disconnect is not engaging properly. This can be caused by worn bearings or a broken shift fork. You can check for worn bearings by grabbing the inner tripot joint(closest to the Front Axle Disconnect) of the right side axle and trying to wiggle it. Movement indicates worn bearings. Even if your bearings aren't overly worn, there is a possibility of a broken shift fork, spring, or other components.

    There is a great guide on the teardown and rebuilding of the Front Axle Disconnect here: http://www.offroadtb.com/articles/tech-docs/front-axle-4wd-disconnect

    There is an alternate way of fixing the shift fork issue here: http://forums.offroadtb.com/viewtopic.php?f=27&t=1227

  3. If you rebuild/replace your Front Axle Disconnect or are 100% sure it is functioning properly and still are at this point in the troubleshooting guide, you may have an internal front differential failure (likely) or broken intermediate shaft (extremely rare, couldn't find an instance of this by searching). Now is the time to make a post in the 4x4 section detailing all the steps you followed in this guide as well as any other observations made.


There you have it. I hope this guide points you in the right direction.

Additions/corrections welcome! :cool:


 

·
Banned
2002 chevy trailblazer_ls
Joined
·
7,255 Posts
Looks like a decent baseline for troubleshooting. You, sir, have earned yourself a sticky. I would assume anyone can feel free to add their own advice and/or repair experience. But let's try to keep the questions to a minimum.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts
How about a step by step for rainier envoy or whatever that use the 4awd system?

And add links to not just fixing the spline disconnect but any other repair how-tos on fixing the actuator or control modules.
 

·
Banned
chevy
Joined
·
1,091 Posts
Discussion Starter #4
How about a step by step for rainier envoy or whatever that use the 4awd system?

And add links to not just fixing the spline disconnect but any other repair how-tos on fixing the actuator or control modules.
The AWD system actually has far fewer points of failure than the selectable system. There is no splined disconnect, actuator or selector switch to go bad. Most of the AWD problems I've read about on here (unfortunately) end up being due to transfer case failure.

I will poke around and see if anyone has serviced the front disconnect actuator itself. When I rebuilt my disconnect, I modified the assembly to never disconnect the front axle, so mine now works a lot like your AWD setup.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts
The AWD system actually has far fewer points of failure than the selectable system. There is no splined disconnect, actuator or selector switch to go bad. Most of the AWD problems I've read about on here (unfortunately) end up being due to transfer case failure.

I will poke around and see if anyone has serviced the front disconnect actuator itself. When I rebuilt my disconnect, I modified the assembly to never disconnect the front axle, so mine now works a lot like your AWD setup.
you might want to look into the awd system, i think its all the same. Im pretty sure i have an actuator, splined disconnect and tccm, just no switch. The system works when the back wheels start spinning it kicks in the front wheels. So they are not always activated.

Mine currently does not work.

To troubleshoot mine i lifted the whole truck off the ground. As the back wheels spun I can hear a fast clicking up front passenger side. I dont know if this is the actuator or disconnect. Next Im going to try to take off the actuator and activate the disconnect myself to see what happens. Unless someone tells me they know exactly whats broke on mine.
 

·
Banned
chevy
Joined
·
1,091 Posts
Discussion Starter #6


This is the diagram for both the selectable (#56) and AWD (#57) disconnect housings. If you look closely at the AWD version, you'll see that there is actually no disconnection medium in it. No actuator, fork, collar, gears etc. Just a sleeve that connects the intermediate shaft and axle.

If you are getting a clicking from yours then my first guess would be stripped splines internally.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts


This is the diagram for both the selectable (#56) and AWD (#57) disconnect housings. If you look closely at the AWD version, you'll see that there is actually no disconnection medium in it. No actuator, fork, collar, gears etc. Just a sleeve that connects the intermediate shaft and axle.

If you are getting a clicking from yours then my first guess would be stripped splines internally.
ouch...

wow ive read alot of topics and all seemed to discuss the disconnect on the rainiers like they were the same. So this buick is supposed be all wheel drive all the time? Ive always heard it would kick in when needed? Last night i looked and seen something that looked like an actuator by the disconnect housing.

So if I dont have all that stuff then are you saying that 57 piece is broke on mine or something in the differential?
 

·
Banned
chevy
Joined
·
1,091 Posts
Discussion Starter #8
ouch...

wow ive read alot of topics and all seemed to discuss the disconnect on the rainiers like they were the same. So this buick is supposed be all wheel drive all the time? Ive always heard it would kick in when needed? Last night i looked and seen something that looked like an actuator by the disconnect housing.

So if I dont have all that stuff then are you saying that 57 piece is broke on mine or something in the differential?

Your AWD does indeed only kick in when needed, but the system itself is always at a "Ready" state vs the selectable 4WD which essentially has an "Off" setting (2HI).

If the noise is indeed coming from the front passenger side, look at the disconnect housing, if it's from the driver side, look to the differential.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts
Your AWD does indeed only kick in when needed, but the system itself is always at a "Ready" state vs the selectable 4WD which essentially has an "Off" setting (2HI).

If the noise is indeed coming from the front passenger side, look at the disconnect housing, if it's from the driver side, look to the differential.
OK thanks.

Is there a repair guide to the all wheel drive disconnect system like the fork style on that off road site?


ahhhh im asking too many questions on this non question asking topic:nono:
 

·
Banned
chevy
Joined
·
1,091 Posts
Discussion Starter #10
OK thanks.

Is there a repair guide to the all wheel drive disconnect system like the fork style on that off road site?


ahhhh im asking too many questions on this non question asking topic:nono:
It's here in a sticky post, so hopefully someone else with similar problems will see it and benefit.

Your disconnect assembly is similar to the selectable disconnect assembly, and the rebuild procedure is essentially the same. You simply don't have a fork, and in place of the two gears and collar, you have a single piece that joins the two shafts.

Unfortunately Compnine isn't listing a part number for that part. All the others are listed in the previously linked article.
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
1 Posts
4x4 random "popping" in front while engaged

Here's my problem, i have had a couple of problems with the 4x4 on my 02 trailblazer. first problem ended up being the TCCM (replaced), 2nd was perceived to be the actuator (replaced). i dont have service lights coming on and it goes into 4x4 just fine and works BUT now while driving (mostly on a grade) the front end has a "pop" at random times that i can hear and feel. it's like the 4x4 is trying to disconnect. a couple of times i've had to stop and go to nutral and back to drive for it to re-engage, other times it stays in 4x4 with the random "pops"... anyone have an idea where to start this next search mission? :confused: this is the first time i've tried to post a question, hope im doing it right...
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Unless your differential is about to break, your popping sounds like an insufficiently engaged collar or gear wear inside the splined disconnect. No options other than removing it and cleaning and regreasing after inspecting everything inside.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts


So heres what I find by my axle on the passenger side. No actuator. In the oreilly and autozone directory it says I have an actuator but I dont see one. Is it somewhere else? If I raise up the whole truck and put it in drive the front driveshaft turns but the wheels do not. It makes a humming noise up front somewhere. The RPMs go from 900 to 600 back and forth. I know its AWD and not the 4x4 but there has to be something that tells it when to kick into AWD right? This isnt looking like an easy fix. I cant believe something would be seriously wrong, the truck only has 70k miles on it! Bad quality.
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
AWD Rainiers don't have an actuator there. The splined disconnect is ALWAYS engaged. The parts stores are wrong. You have a broken differential. I replied in your other thread. One is sufficient.
 

·
Registered
2005 buick rainier
Joined
·
34 Posts
AWD Rainiers don't have an actuator there. The splined disconnect is ALWAYS engaged. The parts stores are wrong. You have a broken differential. I replied in your other thread. One is sufficient.
thanks. parts stores, ebay, everyone is wrong :duh:
 

·
Registered
2003 gmc envoy_slt
Joined
·
50 Posts
In the post under section 2 it doesn't say what to do if you don't hear any sounds only if you don't hear sounds from the front or under you. What do you think that could be, i have no lights on the mode selector ( not even a light for 2 wheel which i'm currently in) and absolutely nothing happens when i switch it to any of the four wheel drive settings. I'm troubleshooting right now, checking wires on the switch and such. All the fuzes test good. Sorry for the long post. Thank you
 

·
Banned
2004 gmc
Joined
·
26,181 Posts
Do your lights on the switch light up when you first turn on the ignition? If yes, then your TCCM, switch, or the wiring between them is bad. If no, then the TCCM may not be getting power even if the fuse is good. Do you have a meter and want to troubleshoot the TCCM connectors yourself? The schematic has been posted but let me know if you can't find it.
 

·
Banned
2004 gmc envoy_sle_xl
Joined
·
1,239 Posts
BTW, the AWD designation on our platforms stands for Automatic Wheel Drive not All Wheel Drive. As was mentioned previously when AWD is selected (or is the standard operating mode), the system is in a ready state to switch in the front axle when rear wheel slippage is detected.
 

·
Registered
2002 gmc envoy_sle_xl
Joined
·
3 Posts
Tranfer case

My transfer case has a "nice" crack (2002 GMC Envoy). Where would be a good place to send it or find one myself and rebuild?
 

·
Registered
2003 gmc envoy_slt
Joined
·
50 Posts
Do your lights on the switch light up when you first turn on the ignition? If yes, then your TCCM, switch, or the wiring between them is bad. If no, then the TCCM may not be getting power even if the fuse is good. Do you have a meter and want to troubleshoot the TCCM connectors yourself? The schematic has been posted but let me know if you can't find it.
I ended up pulling the front console and checking the wiring to the switch which tested good. I hooked up the computer and it said there was no communication with the transfer case module. Before we ripped some more crap apart to check that i decided to go with what someone else had posted about disconnecting the battery for 30 minutes and VOILA, it works. Now i only i wish i would have done that a first, lol. Either way, i got my 4wd back which is great because of all this damn snow we been getting. Thanks for your help :tiphat
 
1 - 20 of 76 Posts
Top