Can 4WD engage in the absence of a working 4x4 control module?

[kmanning]

Is it possible for the transfer case to engage 4WD automatically if the 4x4 control module (behind the glove compartment) is not operational? If the answer is no, could this phenomenon occur if the transfer case is malfunctioning, for example, there is a bad sensor on the transfer case?

BACKGROUND: I believe that the 4x4 control module behind the glove box on my 02 XLT (equipped with control-trac 4wd) is not working and has not been for a long time. I have the classic post-battery disconnect symptoms of no 4wD lights appearing on the instrument cluster upon vehicle startup, and no lights come on on the dash when the buttons for the various 4WD levels are pushed. Also on this forum I read to roll your window down and with key on engine off listen for the sound of the motor on the transfer case as the dash buttons are pushed--heard nothing.

I have the loud popping in the front end upon sharp turns, and I am troubleshooting. My question above is to determine if I can eliminate 4WD from the possible causes. Thanks for any help.

I have spent many hours searching on the forums for the answer to this question, and I do not believe this specific question has yet been answered.

 

[Number4]

I'd say the module is at least intermittently working. There's a TSB for false 4wd engagement on sharp slow turns.
As the front wheels begin to rotate at different speeds, the 4wd kicks in and causes a noise.

 

[wbrudi28]

If say the module is at least intermittently working. There's a TSB for false 4wd engagement on sharp slow turns.
As the front wheels begin to rotate at different speeds, the 4wd kicks in and causes a noise.

an easy way to trouble shoot it, if you're interested, is to do the BWM. it will bypass the whole front part of the drivetrain and you can see if the noise is occurring at the sharp, low speed turns. it won't give you the answer youre exactly looking for, but it could possibly help.

 

[kmanning]

transfer case and electrical inputs

I see that the first step in the TSB is to disconnect all the wiring going to the transfer case.

1) Would this have the same effect as the brown wire modification?

2) Would it also have the same effect as driving the vehicle with the #17 and #18 fuses pulled?

3) Would it also have the same effect as disconnecting the 2 wire connectors of the 4x4 module (behind the glove box)?

Thanks.

 

[Joe in NY]

Yes disconnecting the 4X4 module will do the same. When I installed my new module my car started binding up in turns. Did BWM, all good now.

 

[kmanning]

how do you disconnect the wiring to the transfer case?

The TSB says "disconnect all wiring going to the transfer case" I have found the large wiring harness that attaches above the motor on the transfer case, and I assume that would accomplish this step for the TSB. However, I am not very good at disconnecting these wiring harnesses, and I am afraid I am going to break it. I can feel a tab or something that gives on top, but when I press on it and tug at the harness it does not come apart. Will someone please walk me through disconnecting it? Sorry that I have trouble with such a simple thing, but the last thing I need to do is break something else.

more background: I am trying to absolutely positively remove all electrical inputs to the transfer case (I have to travel to a job site tomorrow and just do not have time to do the brown wire mod right now) so that I can determine if my transfer case is stuck in 4WD. I have read several instances in the forums of this happening. I removed the front driveshaft to see if my popping noise would go away. It did not, and so I concluded that the 4WD was not engaging and causing the noise. But to doublecheck that the car was not in 4WD, I bungee corded a video camera to catch a view of the transfer case yoke (the one that attaches to the front driveshaft) while going for a ride with the front driveshaft removed. I did this first with the electrical inputs to the transfer case the way they normally are (that includes an apparently non-functional 4x4 control module behind the glove box as described in post 1). The video showed the yoke turning. Being unable to disconnect the wire harness, I pulled the #17 and 18 fuses and went for another drive. That video is at:

https://youtu.be/MeY0rLm3D_0

(That is a piece of pink flagging tape tied on so that it will show up better. If you watch until about 2:17 you hear the popping that I am trying to diagnose. )

I would conclude from this video that the vehicle is in 4WD, correct?

Now I am concerned that the transfer case is stuck in 4WD. Is this definitely true given that the #17 and 18 fuses were pulled, or could some electrical signal still be reaching the transfer case causing it to engage 4WD? If it is stuck in 4WD, is there any way to fix it other than a new transfer case?

And with the vehicle stuck in 4WD, are there any components that would have been damaged that would be the likely culprit of the popping noise?

Thank you for your patience with me on this.

 

[wbrudi28]

do. the. brown. wire. mod.

it will disengage all electronic 4wd components.

 

[Number4]

The BWM is more of a 'permanent' mod. Allows user to engage disengage from inside the cab vs. pulling and re-inserting a fuse.

For your purpose, just pull the fuses. Just watch out as the fuse may be for more than one item.

 

[kmanning]

stuck in 4WD

For your purpose, just pull the fuses.

Well, it would appear then that the vehicle is stuck in 4WD. I guess it would be worth it to try a new 4x4 control module to see if that could possibly unjam it before investing in a new transfer case. From what I understand you can only do a manual adjustment between Hi and Lo by removing the motor on the transfer case--doesn't solve the problem of being stuck in 4WD. Joy, joy, joy. If I ever get this straightened out I will certainly be doing the brown wire mod--I don't intend to go through this again.

Thanks to all for your generosity in sharing your knowledge.