02 Trailblazer 4wheel drive won't engage

ZakJacobs

Original poster
Member
Apr 23, 2012
2
I have a 2002 Trailblazer LTZ and I cannot get the 4wheel drive to engage. It won't go into 4hi or 4low. When i move the switch to any position nothing seems to happen. I tried A4wd and 4hi while driving and 4low while in neutral but it just stays in 2wheel. Is this something as simple as the switch or do I have a major task in front of me?
 

davenay67

Member
Jan 16, 2012
217
ZakJacobs said:
I have a 2002 Trailblazer LTZ and I cannot get the 4wheel drive to engage. It won't go into 4hi or 4low. When i move the switch to any position nothing seems to happen. I tried A4wd and 4hi while driving and 4low while in neutral but it just stays in 2wheel. Is this something as simple as the switch or do I have a major task in front of me?

"Roadie....clean up on aisle 5...."

Seriosuly, the Roadie is the guru in this area....he will be along shortly to help....
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
First:

tiphat.gif
Welcome
tiphat.gif


In case you haven't heard:
http://gmtnation.com/f5/welcome-gmtnation-com-heres-story-226/

Have you checked fuse #48 in the rear fuse box?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
1) Do the switch lights all light up when you first turn on the ignition - the "lamp test" process?

2) Does the "Service 4WD" might ever come on in the gauge cluster?

3) Does the 2WD light stay lit over the switch even when you turn it to a new mode like 4HI? Or is the switch dark?

2002 vehicles were notorious for having bad TCCM (Transfer Case Control Modules). Do you have a buddy nearby with a 4WD Trailblazer or Envoy you can swap with for a test?
 

ZakJacobs

Original poster
Member
Apr 23, 2012
2
There is no lights or anything near the gauges that say anything about the 4wd. And the switch is always dark. It doesn't light up at all when i start the vehicle and nothing lights up when the switch turns.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Then you have no power to the TCCM, or the most common 2002 TCCM death. If you find a used one from any Trailblazer or Envoy 4WD from 2003+, they should work fine. If you buy a new one from the dealer or from an on-line GM parts supplier it will need reprogramming from a dealer, and their charge is not fixed, but could be as much as $100, members have reported.

Do you have a meter to rule out a lack of power to the TCCM first?
 

Gavin

Member
Dec 10, 2013
5
roadie this is to answer your checklist
1.Yes it all lights up
2.no fix 4 by light
3.2by light stays on while it trys to go into 4 by but fails

got any ideas please

btw-i just changed my transfer case motor then this happened. its a 2003
 

Gavin

Member
Dec 10, 2013
5
while i was driving in the city and i was switching back and forth to 2by to 4by which was my first mistake and then the 4by just quit and hasnt worked since that and my fix 4by light turned on it would switch to auto but it only kicked in and out real quick sounded bad. Then i got my friend to look at it with his tech 2 and he said it could be the encoder reader so i just bought one on ebay and switched it out tonight and now it wont work at all. Like it tries but always goes back to 2wheel so yeah thats where i'm at.
 

Chief21

Member
Dec 11, 2013
3
I'm having similar problems with my 2007 Trailblazer LT.

Responses to Roadie's Questions:
1. All the lights on the selector switch come on at start up and then go away right away.
2. The service 4wd light is on and will not go away.
3. The switch is completely dark except when at start up.

I replaced the switch recently hoping it was an easy fix there but that did not change anything. I'm wondering if I could have possibly installed it incorrectly? I just unplugged the old and plugged in the new one? Is there more to this process that I'm unaware of?

I checked the #8 fuse under the hood and the #48 fuse under the rear seat, both are good and resetting those did not change anything. I've tried holding the switch in 4hi for 10 seconds with the key in the on position but that also resulted in no change.

Any ideas? Am I looking at needing to replace the TCCM? I don't want to go through all that and still have no change. I'm wondering if when the battery was drained by my wife recently and then having to replace it created any issues. Thanks!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Welcome Chief!

The switch going absolutely dark after the lamp test sure makes it look like a TCCM issue. Or power. The Service 4WD light will come on if the PCM loses communication with the TCCM.

If you only had a local buddy you could swap TCCMs with, you could avoid buying one on speculation or paying somebody with a Tech II tool to do an accurate diagnosis.
 

Chief21

Member
Dec 11, 2013
3
Yeah I wish I knew someone in the area that we could do the swap out on, unfortunately there are none that I'm aware of. Would I be able to take it to the local Autozone or a similar place and have them run a diagnostic check to give me the code from the service 4wd light? Or is that something I have to go to the dealership to do? Sorry, might be a dumb question but I've been fortunate enough in my life to always have my dad working in the auto parts industry previously so he took care of these things for me up until he passed away a few years ago.

I know I can purchase the TCCM online pretty easily and at a fair price, just not sure what exact part number it is and how difficult the installation is, particularly for a guy that's only moderately experienced in car mechanics.

Thanks for your help so far!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Parts store code readers won't tell anything about deeper problems other then PCM codes. And a dealer or an independent mechanic with a Tech II won't be able to tell anything if the module is bad and can't communicate.

If you get an Ebay TCCM, make sure it's a 2003+ (they are all interchangeable) as long as it's been programmed for a TB or Envoy (true 4wd, not AWD like the Bravada).

Part numbers and the location of the TCCM above the driver's left knee have been posted in many other threads here and on trailvoy. The replacement is trivial because of the location.
 

budwich

Member
Jun 16, 2013
2,075
kanata
Chief21 said:
I'm having similar problems with my 2007 Trailblazer LT.

Responses to Roadie's Questions:
1. All the lights on the selector switch come on at start up and then go away right away.
2. The service 4wd light is on and will not go away.
3. The switch is completely dark except when at start up.

I replaced the switch recently hoping it was an easy fix there but that did not change anything. I'm wondering if I could have possibly installed it incorrectly? I just unplugged the old and plugged in the new one? Is there more to this process that I'm unaware of?

I checked the #8 fuse under the hood and the #48 fuse under the rear seat, both are good and resetting those did not change anything. I've tried holding the switch in 4hi for 10 seconds with the key in the on position but that also resulted in no change.

Any ideas? Am I looking at needing to replace the TCCM? I don't want to go through all that and still have no change. I'm wondering if when the battery was drained by my wife recently and then having to replace it created any issues. Thanks!

Before you do anything more, I certainly hope you are checking your fuses (and the fuse holder) with a meter.... your eyes can't see voltages and resistances.
 

Chief21

Member
Dec 11, 2013
3
Roadie - Thanks for the help, I was pretty sure that I would have to go to the dealership to get any reading and I'm pretty sure after reading everything that the TCCM needs replaced. Thanks for the info on what to look for.

I have not done a voltage check on the fuses or the fuse holder but I have replaced the fuses with no luck and I'm not having any other electrical issues aside from this so I'm assuming the holder is still good? Maybe I shouldn't assume that?
 

budwich

Member
Jun 16, 2013
2,075
kanata
The fuses in question only deal with the "drive system" so you aren't going to see anything else affected. Having said that one fuse lights lights... :smile: so yours are working so that is a "good ass..." but the other does "physical work" so is your "ass... " good, maybe.... :smile: Anyways, it was more of a "hint" to get you to get a meter and check a few things as there is some wiring involved which replacing fuses isn't going to do much for (ie. broken wire). It sounds like you are going to continue in the parts replacement mode, moving towards the next best "guess" which is fine but maybe not cost effective. But maybe in this weather, better especially if the dealer is doing it for you... :smile:
 

Gavin

Member
Dec 10, 2013
5
Hey Gavin here ran into a bigger problem I can go in all gears but it won't move forward or backwards the switch trys to go into auto or 2 wheel but doesn't lock and the light just quits anyone have an idea please need help here.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Gavin said:
Hey Gavin here ran into a bigger problem I can go in all gears but it won't move forward or backwards the switch trys to go into auto or 2 wheel but doesn't lock and the light just quits anyone have an idea please need help here.
There seem to be THREE separate incidents going in this one thread? Man, I'm about to separate them all out into their own sessions.

In any event, Gavin.....when you say "won't move forwards or backwards" are you saying the engine is no longer connected to the wheels? That could be a totally broken transfer case, often caused by not changing the fluid every 50K as required. Or it could be a bad transmission. I strongly recommend you get it towed to a trusted transmission shop for diagnosis. This is nothing for a backyard DIY mechanic to be working on, unless you've changed large items like transfer cases before. It's not a simple electrical control problem, unless you can describe your symptoms with a bit more detail.

When you say "gears" do you mean transmission gears, or transfer case 4WD modes? When you say "go" in all gears do you mean the vehicle moves as expected, or the shift lever "goes" into the desired gear but the vehicle doesn't move? When you say the "Switch tries" to go into a new 4WD mode and the light quits - WHICH light quits? The mode you're moving away from or the mode you're trying to change to? And does it blink first? And by "quit" do you mean go dark, or quit blinking?

The troubleshooting flowchart has a lot of possibilities, and every detailed observation is necessary to help us help you.
 

Gavin

Member
Dec 10, 2013
5
I was driving on the highway today and the engine was still running but tires turning and i was just reving the engine so i pulled over drive didnt work neither R 321 everything stopped like its only in neutral and the switch inside light blinks but then goes to dark and when i put the vehicle back in park it makes like a grinding noise every time so thats what is happening.

Do you think it might be my tccm or am i not that lucky
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I guarantee it is not your TCCM. Assume you're getting it towed.

If it's making a noise in PARK without the vehicle moving it's not even your transfer case.

Santa delivered a lump of coal this year. Wicked sorry.
 

budwich

Member
Jun 16, 2013
2,075
kanata
:-( when was the last time you checked to see if you have got transmission fluid and its the "right color"?
 

parisien1

Member
Feb 20, 2014
2
the roadie said:
1) Do the switch lights all light up when you first turn on the ignition - the "lamp test" process?

2) Does the "Service 4WD" might ever come on in the gauge cluster?

3) Does the 2WD light stay lit over the switch even when you turn it to a new mode like 4HI? Or is the switch dark?

2002 vehicles were notorious for having bad TCCM (Transfer Case Control Modules). Do you have a buddy nearby with a 4WD Trailblazer or Envoy you can swap with for a test?

I just purchased a 2003 trailblazer LT. 4.2 6 cyl. and the switches all light up when I first turn the ignition on.
The service 4wd light is on
the 2WD light stays lit when I move the switch and the light over which ever position I choose just blinks
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
parisien1 said:
I just purchased a 2003 trailblazer LT. 4.2 6 cyl. and the switches all light up when I first turn the ignition on.
The service 4wd light is on
the 2WD light stays lit when I move the switch and the light over which ever position I choose just blinks
Welcome!

Did you get a pre-purchase inspection that noticed this fault?

Any maintenance records that showed the transfer case fluid was changed at the very important 50K mile intervals?

Did you get it from a dealer that advertised it as a 4WD vehicle and it is not currently possible of BEING a 4WD vehicle? (You may have legal recourse).

This may be a new record of number of members posting about the same issue in one thread. What have you done from the recommended troubleshooting flowcharts besides move the switch and look at the lights? Are you a DIY'er ready to remove the encoder motor from the side of the transfer case and see how it behaves in midair, not connected to the transfer case mode shaft?
 

parisien1

Member
Feb 20, 2014
2
the roadie said:
Welcome!

Did you get a pre-purchase inspection that noticed this fault?

Any maintenance records that showed the transfer case fluid was changed at the very important 50K mile intervals?

Did you get it from a dealer that advertised it as a 4WD vehicle and it is not currently possible of BEING a 4WD vehicle? (You may have legal recourse).

This may be a new record of number of members posting about the same issue in one thread. What have you done from the recommended troubleshooting flowcharts besides move the switch and look at the lights? Are you a DIY'er ready to remove the encoder motor from the side of the transfer case and see how it behaves in midair, not connected to the transfer case mode shaft?

To answer your questions, No, No, No, and Maybe. I purchased it from a private seller. It was a good price and the TB runs fine(minus the 4wd not engaging) and I didn't have much time to really wait around on the deal that I got because there was about 5 other people coming to look at it the next day. I had to make a decision quickly. I bought it knowing it needed some work. I wouldn't even try to claim that I'm a mechanic, but have some mechanical skills. I think I could remove the encoder motor(I thought it was a transfer case motor).
I guess my post was originally in hopes that the way the lights acted and the service 4WD light being on you might have a pretty good guestimate of what it might be Or ways that I can test the switch, motor, and TCCM before I go as far as trying to replace the transfer case.
 

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