Transfer Case 4WD Problems (detailed)

I have read through 80% of the form looking at posts related to this issue, there hasn’t been too much detail since most people have opted to take this condition to the dealer and let them sort it out.

The condition I am seeing on my 2002 TB started off as an intermittent service 4WD light. Issues with shifting then started later, where the system may or may not shift into what you have selected. Today the transfer case will not shift out of 4HI, or AWD.

What I have found out on my own:
1) The Owners Manual is a waste of time. It states that the reason for the light is a problem with the fluid level. In some cases this could be the problem. Not with mine.
2) The shifting module wiring isn’t in the Haynes or Chilton manuals, just the position lighting. I know that after researching the shifting module, the unit has 7 wires. From the manuals I see that 4 are “position” indications to the switch. From the system description the other three need to control the shifter, CW, CCW and Ground.
3) I assume that when other people talk about flashing a computers memory related to this issue, they mean the Power train Control Module. Even though I couldn’t find the wiring, I am pretty sure that this is what sends out the commands to the shifting module telling it what direction and how far. I slightly disbelieve that changing software in this box would really change anything, other than how the AWD works, I mean you are either in 2WD, or 4Hi, or 4Lo.
4) Looking around the transfer case, I think I have identified the other wiring as speed sensors, nothing to do with the shifting. So all of this is between the command (the rotary switch), the computer (control), and the shifting module (the work)
I am pretty sure that I have a bad shifting module from what I see. I also believe that motors like this will degrade getting worse, while computers usually just stop working.
I have also taken the shifting module off the transfer case and tried running it. The thing only would move between two positions. I also checked the transfer case lever movement and was able to move it into a couple different detents.
Don’t hit the shifting module with a mallet! The 4 motor brush springs are delicate little things and will easily “pop off or out of” the brush grove. No power to the motor brushes means it will not work.

If you have had experience working on the transfer case, let me know if I am going down the right path. These things are expensive, $260.00! Autozone can get them if you don’t want to use the dealer. However the track II fluid is a dealer item and a transfer case caries about a quart and a half. Good luck if you are reading this and you have the same problem.

The two most common causes for 4x4 concerns on the GMT360 chassis are either the dash switch or the transfer case encoder motor. I have not torn into either, but from what I understand, there is a postion switch the TC encoder motor reads that needs to match the position [switch] selected by the dash rotory switch. I don't know how to test these independantly. There is no 'all wheel drive' with this drivetrain. It's automatic 4wd (A4wd) where the front drive train kicks full on or full off when rear wheel spin is detected.

Joel

I have a similiar issue were the Service 4wd light would come on and you couldn't use the switch to switch to 4Wd. It was a module. I will look throught my dealer receipt to see what it was. Of course the dealer didnt find what the problem was until I went into my extended warranty and had to pay the $100 deductible. Will it was still under the 3/36 they kept saying they couldn't find anything wrong.:banghead:

Ok found the receipt. They replaced the transfer case control module. the explanation was that it was falling asleep. hope this helps. total cost for work at dealer was $323. :eek:

Thanks for the responses back on this, your information provided assures me that I am going into the right direction. There are a few components that don’t match up however as I piece things together from the manual and what little I have out of the wiring diagram I am pretty sure that I can make the following statements:
1) A transfer case control module is the same thing as a transfer case shifting module.
2) A transfer case encoder module needs to be part of the shifting/control module. As I found in the wiring diagram four of the wires (out of seven) provide position back to the switch for actual position from the shifting/control moudule. I agree that when you move the switch, the new position lighting selected starts to flash, this is a “hey wait until I get there” indication. Once the motor has overcome gear disengagement from the 2 or 4 wheel drive position started, it will re-engage in the new commanded position where this encoding module switch will say “hey it is in the right position, stop driving the shifting motor and light the light solid”
I am also trying to remember, I don’t use the 4LO that much. I think that the motor needs to drive past the 4HI position from 2HI to get to 4LO, so you will see 4HI flash as the motor moves the gearing past that point, then to 4LO.

Anyhow, if the motor can not move the input spline that shifts the actual gears in the transfer case, it will never get to where it has been commanded to go, the power train control module sees this and posts the 4WD service light.

I also see where this automatic 4WD thing comes in, kind of why you need all of the speed sensors on the tail shaft of the rear drive line and one on the output to the forward axle. The transfer case has engaged both drive lines, with the power train control module looking for a slip in the rear axle, it will then tell the forward axle actuator to engage or disengage when out of the slip.

Part should be in tomorrow, so I will know then. And hey the $323 price tag on a part that I find costs about $250 isn’t all that bad. They probably went right to it, at dealer rates of 80 an hour, to get the thing up on jacks, remove the 7 bolts holding the rock guard, pull the 4 bolts holding the shifting control module on and reverse, that isn’t bad.

Once you get to the end of one of these ordeals you feel so much smarter then when you started!

The problem turned out to be a wire in the spade connector going to the shifting module not properly seated.

I ended up taking it to the delar to figure this out, they can access the codes from the computer to have an idea where to start. Without a wiring diagram the technician did clarify the components and system operation. There is a encoder module/computer that controls the shifting module. This was suspected as being bad from the code that it was receiving. However upgrading the encoder moduled didn't fix the problem, so the tech had to get into the system a little further until he found the bad wire.

FYI, these are Feb 2007 prices at the dealer in Tucson:
$45 for initial troubleshooting and reading the codes.
$94 to upgrade the software in the encoder.

Dr.L, was this spade connector on the T-case encoder motor & exposed to the elements? Out of curiosity, I'm trying to figure out where this supposed control computer is. From any of the posts I've read, or poking around I've done, I thought any 'electronics' were self contained within the transfercase or dash swtich.

Joel

The loose spade pin was on the connector going to the shifting module. This connector is about 8" from the shifting module, swings above the transfer case and secures to a clip right above the transfercase. So it is out in the elements, kind of.

I don't know where the elusive encoder module is located at. There definitly is a big hole missing in the Chilton book on the operation of this system.

Thanks for the info. I know there is a position switch associated with the encoder motor/ shifting module. Not sure if it's on the drive end of the encoder motor, or burried within the transfer case. As far as a seperate transfer case mode computer? I dunno. I was under the *assumption* everything was tied into the powertrain control module under the hood, bolted to the intake manifold (on the 4.2L).

Joel

Rodeo, I was looking at that module and the three connectors on it. I guess when I have some free time, I was going to look for matching wiring coming up to it, the three what I call command wires are not coming from the switch, they got to be coming from this shifting encoder.
I think that part of that module is dedicated to the thrasfer case shifting, what they call the shifting encoder. I identified all of the wires on the transfercase, two speed sensors and the shifting module. So somewhere the output from the dash switch is being looked at, then commanding the shift module to move, and if there is a disagrement, this box then tells the computer to indicate the 4wd service light.

I couldn't tell if any of the bundles were disturbed during the troubleshooting at the dealer. It is now just something