Service 4WD

PProph

Original poster
Member
Dec 7, 2011
220
Hey all, I used the search but couldn't find a problem quite like this (go figure). Every once in a while when I turn my TB on (03 LTZ ~190000 kms) I get the Service 4WD light, and none of my options light up on my dial (usually the 2HI is lit up obviously). Also I can't switch to anything but the 2 HI I'm in. Hasn't happened to me for awhile, but we're on a trip through the rockies yesterday and kept pulling off to take pictures, this happened after one of those restarts. I figured it might have something to do with the fact that I'm obviously pushing the tranny a little harder with all the inclines and speed changes. But then to get the problem to disappear, I pulled over, stopped, shut off the vehicle, pulled out the key and opened the door so that everything shut down. While it was off I flipped my drive dial back and forth a few times (between 2HI/A4WD/4HI/4LO). Back in to 2HI and I started up again, things are normal, Service 4WD light is gone. So I'm wondering, perhaps this isn't something very serious with the 4WD, but more so with the electrical or even the dial itself? What would be the best course of action to diagnose something like this? I very rarely use the 4WD beyond winter driving, and even then I don't use it a ton, but I definitely want to know it's working.

A little bit of recent history on the TB, I bought it March 2011 and shortly afterward I took it in with some 4WD problems, turns out they had the wrong type of fluid in the transfer case, the previous owner's backyard mechanic didn't do enough research. So all of my fluids are now good and the parts should be in good working order. I'm hoping it's electrical and ideally something to do with that dial in the dash, because that should be a simple enough fix I think.

Elsewise the TB's running great, I need to do a couple of fixes (heated seat elements, cluster motors are shot for the oil pressure and temp gauge), but nothing serious. I switched to AMSOIL this year and with the help of this site also diagnosed and replaced my water pump in the spring. Definitely still enjoying becoming a TB owner!
 

McGMT

Member
Jun 17, 2012
621
PProph said:
Hey all, I used the search but couldn't find a problem quite like this (go figure). Every once in a while when I turn my TB on (03 LTZ ~190000 kms) I get the Service 4WD light, and none of my options light up on my dial (usually the 2HI is lit up obviously). Also I can't switch to anything but the 2 HI I'm in. Hasn't happened to me for awhile, but we're on a trip through the rockies yesterday and kept pulling off to take pictures, this happened after one of those restarts. I figured it might have something to do with the fact that I'm obviously pushing the tranny a little harder with all the inclines and speed changes. But then to get the problem to disappear, I pulled over, stopped, shut off the vehicle, pulled out the key and opened the door so that everything shut down. While it was off I flipped my drive dial back and forth a few times (between 2HI/A4WD/4HI/4LO). Back in to 2HI and I started up again, things are normal, Service 4WD light is gone. So I'm wondering, perhaps this isn't something very serious with the 4WD, but more so with the electrical or even the dial itself? What would be the best course of action to diagnose something like this? I very rarely use the 4WD beyond winter driving, and even then I don't use it a ton, but I definitely want to know it's working.

A little bit of recent history on the TB, I bought it March 2011 and shortly afterward I took it in with some 4WD problems, turns out they had the wrong type of fluid in the transfer case, the previous owner's backyard mechanic didn't do enough research. So all of my fluids are now good and the parts should be in good working order. I'm hoping it's electrical and ideally something to do with that dial in the dash, because that should be a simple enough fix I think.

Elsewise the TB's running great, I need to do a couple of fixes (heated seat elements, cluster motors are shot for the oil pressure and temp gauge), but nothing serious. I switched to AMSOIL this year and with the help of this site also diagnosed and replaced my water pump in the spring. Definitely still enjoying becoming a TB owner!


Flipping the switch like that is probably one of the first things you would be told to do on here.. Dust n dirt and everything else gets in it on the contacts and a fast back and forth tends to clean them out. More than likely you need to change out that switch, I am putting my vote for it.
 

freddyboy61

Member
Dec 4, 2011
276
This also happened to me today, out of the clear blue sky. Removed the #48 fuse (4WD) in the rear fuse panel, and reinserted, selector switch lights came back and Service 4WD indicator went off. May be poor contact on fuse or TCCM went stupid.
 

Voymom

Member
Feb 3, 2012
2,523
I had the same issue last winter, we wiggled a few wires and found there was a loose connection. Once we fixed the connection it worked fine. Hope this helps!
 

PProph

Original poster
Member
Dec 7, 2011
220
these are the types of ideas i was looking for, will fiddle around with it when i get home. thanks!
 

tnmurdock

Member
Jan 8, 2013
2
My 02 TB seems as of late, to be on it's own time. I can drive for hours and no problems. Then a few times around town and the service 4wd light comes on and it drives like it's in 4wd. Next morning, all back to normal. when it happens the lights on the switch blink on and off and then the 4hi and lo stay lit. Help?

220 miles regular service
 

The_Roadie

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

If you've been regularly cleaning your switch (monthly running it CW and CCW 50-100 times) then I'd suspect the TCCM. If you haven't cleaned the switch by exercising it, try that first. Secondly, buy a new switch - they're relatively cheap even at the dealer, after a 2005 redesign for better reliability. If that doesn't cure it, 2002 were notorious for bad TCCMs, and you can find a used one from any 2003+ 4WD vehicle (trailblazer or envoy, not a bravada) and it's plug and play.
 

tnmurdock

Member
Jan 8, 2013
2
the roadie said:
Welcome!

If you've been regularly cleaning your switch (monthly running it CW and CCW 50-100 times) then I'd suspect the TCCM. If you haven't cleaned the switch by exercising it, try that first. Secondly, buy a new switch - they're relatively cheap even at the dealer, after a 2005 redesign for better reliability. If that doesn't cure it, 2002 were notorious for bad TCCMs, and you can find a used one from any 2003+ 4WD vehicle (trailblazer or envoy, not a bravada) and it's plug and play.

Is there a part number on the switch?Thanks so much for such a quick response
and I have never cleaned it
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Dorman makes aftermarket switches, and ANY parts store will sell you one even if you don't know the part number. Same for the dealers. They have computers to look them up. I think people think they need part numbers about 10X as often as they really do.

In case you have some need I'm not aware of, here's some numbers:

GM Part Number 25965895
Dorman Part Number 901-064
 

Royalwapiti

Member
Jul 16, 2012
82
My 2006 4x4 Service light came on. The lights on my switch went out.

I replaced the TCCM with one from a salvage yard. It too was an 06 Trailblazer. It made no difference. 4x4 service light is on and the switch lights are OFF. And it doesn't go into 4x4. I installed a new switch(From NAPA). It made no difference. 4x4 service light is on and the switch lights are OFF. And it doesn't go into 4x4.

The #8 fuse under the hood is intact and was reinstalled. I pulled Fuse #48 from rear seat for 30 seconds and reinstalled.

Any other things to look at? Is there anyway to test the TCCM to see if it is good? Will disconnecting the battery again do anything?

I suspect this came about due to a battery change about a week before problems started.

Thanks for any help
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The TCCM can be tested by a GM Tech II tool. Can cost $$ to have a mechanic or dealer use theirs to troubleshoot the system.

Typically, the Service 4WD light comes on if the PCM can't talk to the TCCM. Might be power or data communication wiring issues. Can you probe voltages at the TCCM connectors if somebody posts the schematics?

Do the switch lights stay dark even at the initial power-on time during the lamp test on the dashboard?
 

Royalwapiti

Member
Jul 16, 2012
82
All the 4wd switch lights light up momentarily during the power-up time when the ignition is turned on. Then go off.

I have a Fluke multimeter, can test voltages. I also have the knee bolster off and the side cover off the dash. (Wish I had known I could pop that side cover off the first time I put the TCCM in - much easier access.)

Can I just take my TCCM in to them for testing or does it need to be on a vehicle? I dislike the local stealerships and avoid at all costs. My local mechanic has a Tech II, is that all that is needed?

I spent some time today fingering and feeling around the TCCM connectors trying to invoke a response from the service light. I disconnected the battery and reconnected. Nothing.

Thanks Roadie
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Royalwapiti said:
Can I just take my TCCM in to them for testing or does it need to be on a vehicle?
They will insist you bring the vehicle in to them.
I dislike the local stealerships and avoid at all costs.
A man after my own heart. I didn't START off thinking that way, but years of abuse changed my mind.
My local mechanic has a Tech II, is that all that is needed?
Should be.
I spent some time today fingering and feeling around the TCCM connectors trying to invoke a response from the service light.
Here's the schematics and connector drawings from the manual.

tccmschematic1.jpg


tccmschematic2.jpg


tccmconnectors1.jpg
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Your 5V reference from the TCCM to the encoder motor was zero, so it's most likely the TCCM but there's a small chance that wire is shorted to ground in the harness or in the encoder motor. Pulling the connector at the encoder motor will help you troubleshoot that.
 

Royalwapiti

Member
Jul 16, 2012
82
Hello The Roadie,

I tested the leads coming from the TCCM to the Encoder motor. I have 5v on pin A, small voltages on the motor control terminal pins and 14v on the F pin.

Appears the TCCM is cranking out the correct voltages.

Am I looking at replacing the Encoder Motor?

I already bought a TCCM at salvage yard for $65, it didn't fix the problem. The salvage yard will return it and trade me for the encoder motor. That's a good deal.

Thanks
 

Deviation

Member
Mar 25, 2012
19
Royalwapiti said:
Hello The Roadie,

I tested the leads coming from the TCCM to the Encoder motor. I have 5v on pin A, small voltages on the motor control terminal pins and 14v on the F pin.

Appears the TCCM is cranking out the correct voltages.

Am I looking at replacing the Encoder Motor?

I already bought a TCCM at salvage yard for $65, it didn't fix the problem. The salvage yard will return it and trade me for the encoder motor. That's a good deal.

Thanks
What year was the TCCM from? I only ask because it took two TCCMs before I got one that worked. First was from a 2002 and was apparently dead (didn't realize this until I swapped the switch). Second one was from a 2003 TB and worked great. The '02 TCCMs are problematic.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,159
Brighton, CO
Once you get past the TCCM, and if that doesnt fix the problem, there are 2 other known issues..

1) The front axle actuator motor are a known problem. I am currently having this problem

2) Per GM, another problem is the ignition switch isnt transferring the correct amount of voltage. GM swore up and down this was my problem, and it wasnt.
 

Royalwapiti

Member
Jul 16, 2012
82
Deviation said:
What year was the TCCM from? I only ask because it took two TCCMs before I got one that worked. First was from a 2002 and was apparently dead (didn't realize this until I swapped the switch). Second one was from a 2003 TB and worked great. The '02 TCCMs are problematic.

The TCCM came from a 2006 model, same as mine.

I took it in for troubleshooting by the dealer. They didn't tell me much. They think the transfer case is bad. I bought one at a salvage yard, the old one is out, I am waiting for a new sensor connector as I didn't get it disconnected when i dropped the transfer case. It pulled the wires out of it. Dealer wants $53 for a simple connector with pigtail. I ordered some online as I broke the holding tab off another.

Maybe this weekend I will know if it was the transfer case.

I think the dealer would have found the faulty ignition. Not sure about the actuator.
 

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