Weekend Report...

I checked the TCCM and found no corrosion on (or in) the connectors. I did, however, see some rust on the holding braket. So, thinking there may be water damage inside the TCCM, I removed it and inspected it. No water damage found. The TCCM looks good, all the way around. Of course, I have no idea ifthe TCCM isworking properly.

I also checked the wires and connectors leading to the TCCM (behind the glove box). All looks good there.

I revisitied the connectors at the transfer case (encoder) motor, all fuses and relays (that I am aware of), the vacuum actuator. Again, all looks good.

In short, I see no visible culprit. I'm wondering if you all can help me to identify the most likely candidate for replacement. So far, I have a vote for the TCCM and a vote for the encoder motor. The codes I have seem (to me) to point to the encoder motor. But, I recognize that could be a mask.

Also, are there any test methods I can perform to verify proper operation of a component in question? It's seeming difficult for me to test anything...because I can't DO anything with the 4wd. I cannot test the vacuum actuator...because I can't seem to tell it to move. I can't test the encoder motor...because I'm no longer tellingit to move (I believe). I had read (in my link in a previous thread) that you can test pins on connectors for proper voltage...but will that work if I'm not "talking" to the encoder motor? I'm thinking not.

Thanks in advance for any pointers.

Icarus

 

More info:

I'm not sure if the 4wd needs to go through a "drive cycle" like some of the other components, but...

It's been a couple days since I've last been back through the 4wd system, and now it seems to be consistently doing things it has not done before (ie: the symptoms and characteristics of the problem have significantly changed). Now, despite the remaining "service 4wd" light on the gauge panel, the 4wd selector switch is responsive. I CAN transfer from 2HI to AUTO 4wd. I can hear the transfer, I can feel the transfer, and the transfer is affirmed by the selector switch lights.

However, I CANNOT transfer from 2HI to 4HI, or from 2HI to 4LO. Now, during such an attempted transfer, the selected mode blinks 5 or 6 times (on the 4wd selector switch) and eventually returns to 2HI. But, even so, the 4wd selector switch remains responsive. Previously, a failed transfer attempt would result in a completed unresponsive (and blank) 4wd selector switch.

I want a reality check and some feed back here...

I've hear that certain parts of the 4wd system are ~actuated~ by different components. Something ~like~...AUTO 4wd is brought in by vacuum and 4HI and 4LO are brought in by the encoder motor. I can't remember if that's exactly right or not...but it was something like that. Point is...I think that, with these new characteristics, I have a much better chance (with some help) ofseperating symptoms and isolating problem components.

Here's what I'm thinking so far...

The system may not have passed it's startup self test...because I still have a "service 4wd" light on the gauge panel. But, IWONDER ifthe TCCM MUST be working, because I can transfer in and out of AUTO 4wd. If the TCCM was shot, I shouldn't be able to anything at all...right? I think the transfer case MUST be OK, because I can engage the front wheels.

In order for me to say yah or nah on the vacuum switch, vacuum actuator, and encoder motor...it would help me to get some clarification on how the modes are seperated, in terms of actuation and operation.

Of course...the lingering questionsare "what's changed?"..."why are the symptoms different now?". The only REAL things I did last time through was disconnect the battery and the TCCM and reconnect them.

Let me know what you all think!

Thanks,

Icarus

 

Is there a flow chart somewhere...."check this, if this, then this, if not, then that". (not the DTC 002 & 004 chart...I don't have those)

I can't be the expert here on this stuff...I just can't be.

Anyway...in case anyone is interesting in an update...for reference...(because I have the psychological need to believe my pain will help someone else in the future)

I did find, by mistake, that the TCCM did not have a good chassis ground. I think this is why I had NO COMMUNICATION for a long time...the TCCM wasn't even powered. Taking the TCCM out, moving things aroung, cleaning contacts, etc...re-established ground.

That was only part of my problem...but I would say a #1 or #2 thing to check for people having this problem (start with inspection of TCCM and vacuum system).Now that the TCCM is powered, I can transfer in and out of AUTO 4WD...but not 4HI or 4LO. These specific symptoms, along with the OBDII codes lead me to the transfer case motor. I bought one...and will, hopefully, be installing it this weekend.

I would welcome any tips or tricks for getting the old one out. The space available to work is very small. I've heard the front drive shaft needs to come out to make this a less difficult install...I'm planning on doing that.

I hope I'm on the right track here. Any ping from the outside world would be nice.

Thanks

Icarus

 

I changed the servo motor out this weekend. The job went fairly well...and did correct the problem.

So for the sake of referrence...

I DO think that this particular set of symptoms, as described by....

"the Service 4WD light stays on from initial crank. The control switch (dash) blinks all lights once for just a millisecond, but the normal self check clicking and light patterns are not there."

...is an indication that the TCCM is not properly powered. IF I had to build a troubleshooting flow chart to help others work through the problem and isolate a problem component, it would look something like this (less obvious notes, ie: when the same fuse continues to blow again and again):

1. Check proper fuses
a. IF bad fuse found- replace fuse
b. If no bad fuse found - continue

2. Disconnect battery and check all vacuum lines and electrical connectors for abnormality
a. If abnormality found - correct abnormality, reconnect battery, and drive the vehicle
i. If symptoms change - re-evaluate problem (did not personally encounter this set of circumstances)
ii. If symptoms do not change - continue

3. Disconnect the battery, and inspect the TCCM for any abnormality in the connectors or chassis ground.
a. If no abnormality found - consider TCCM replacement
b. If an abnormaility is discovered - correct abnormality. Reconnect TCCM and battery, and drive the vehicle
i. If the TCCM does not become responsive - consider TCCM replacement
ii. If the TCCM becomes responsive (ie: 4wd selector switch becomes responsive, you hear relays, etc.) - continue

At this point, you have to take a look at how the selector switch is responding to commands, what is responding succesfully, and what that means about what ~things~ are working and what ~things~ aren't. This will likely point you (at least it did point me) toa specific component or components.

In my case, I was able to transfer from 4HI to AUTO 4WD and back. Which meant, to me, that the TCCM was working, the transfer case was good, and I've got vacuum. So...I targeted the servo motor.

Hope this helps others.

Icarus

 

hello all just wanted to add a bit more info to this I recently bought a 2000 jimmy for my wife. it has the same 4wd shif problems as have already been talked about. I noticed when i grab the stalk of wires on the TCCMand yank it shifts (bad wiring). I went to the local dealer and was told this is a comen problem. the root cause is bad wiring, and bad placement of the computer. the computer and wires collect mosture, the wires carrode which shorts out other parts of the system IE the computer and servos. so if all you have done is replace partsit might be a good ideato compleatly dissasemble your conectors and clean them. Its a pain and it will take the better part of an hour or two but it may save you a few hundred $$. ive looked at a few of my friends blazers also, all of them had a problem with carrosion. it may have to do with where I live, upstate NY lots of salt on the roads means lots of water and salt on the floor in the winter, its not a good thing for the wiring. Im really a jeep guy at heart and jeep cherokees 97-98 had the same problem with the airbag computer under the drivers seat, but that got a recall to replace and relocate,not a tsb like the 4wd in the blazers have. hop this info will save some of you some money. To fix my proble I ended up at the junk yard where I cut off a set of connectors from a 99 blazer along with about 6 inches of wiring. I then cut off my pigtails and sodered on the pig tails from the junk yard end of problem. Also GM/GMC does not offer a new pig tail you have to buy the entire dash wire set. I have a 2000 gmc jimmy 4 button 4wd and the pig tail from a 98 and up 3 button will work all you need to do is shave off a thin pice of plastic andrearange the wires to match yours and splice. the 98 plug is a 30 pin connector and has 25 wires same as my jimmy but the wires are in different places so i just rearanged them and spliced.

 

Have the same problem as you guys with the 4wd switch not lighting up and workin for a milisecond when i turn ignition on. I have already gone threw a few steps. First thing I got was a TCCM from a junkyard. I then got my hands on a TECH 2 scan tool. Now with the TCCM that was in my 2001 blazer I have a C0308 code in current DTCS. With the junkyard TCCM I have a B2725 Active transfer case swith malfunction under Current DTCS. Now with the original TCCM when I go to turn the Motor on manually with the Tech 2 it tells me a relay or motor fault is detected. When I have the Junkyard TCCM in I can go and put it in any mode I want with the Tech 2 and it will work fine. Now the only problem is it wont work with the TECH 2 disconnected by pushin the buttons it will only work manually with me doing it on the tech 2. The only code I have under current is B2725 Active switch malfunction. So I am not sure where to go from here. It seems like I needed a TCCM and something else. Oh and the first thing I did was buy a new switch trying the easiest thing first. I am starting to think it needed a switch and a TCCM. Any input is appreciated. Thanks.

 

Mine turned-out to be a TCCM ($725 including diagnostics and labor).

 

$725... Holy CRAP!

 

mine was $450