4x4 Control Module...VSS....BOTH? NEITHER? HELP!

[Viol8R]

Morning all. Been reading these forums for a while now and have gained a metric ton of knowledge from it. INVALUABLE!
I too have been experiencing the dreaded 4x4 lite flash scenario. I will be very detailed about what has been going on, so please bear with me.

I have a 2002 Explorer EB. Recently I have had mainly the 4x4 Hi lite blink. There have been instances upon startup though that the 4x4 Lo will come on and stay illuminated (on the instrument cluster not the button). AND sometimes neither will come on. At certain points the truck will not engage at all in ANY gear. When this would happen, I would have to push the Hi & Lo 4x4 buttons in order to get it to engage. After it would eventually engage everything seemed to run fine until next time the 4x4 Hi lite would flash and the cycle would begin again. Now keep in mind that the flashing and the engagement problems do not happen every time. Sometimes she’ll start and everything will run normal. On a side note: during one of my test runs the speedometer went haywire and was registering incorrect speeds. Thus, leading me to believe it might be the Vehicle Speed Sensor.

Reading different possible causes decided (naturally) to start with the cheapest. I climbed under and located the two sensors on the transfer case. I removed and cleaned the minimal amount of buildup on them. I thought that these were the input and output speed sensors (VSS) but they look nothing like the replacement ones I have seen at auto parts stores. These two are angled at 90 degrees on the inside of the transfer case vs the straight type sensors that I have seen. Also, these are “hard-wired” into the harness vs a clip connector types. The cleaning did nothing to rid the problem.

The next step I took was to remove the battery cables to reset the computer. I climbed back under the truck to put the aluminum shield back over the shift motor, and while there decided to clean the grounding terminal attached to the shift motor harness “just in case”. Initially it did not look corroded so I did nothing to it. After about 25 minutes I started the truck back up and lo and behold both Hi and Low 4x4 seemed to be working again. I drove it numerous times that afternoon and intermittently testing both 4x4 engagements. While testing you could hear the 4x4 control module “clicking” when shifting into and out of Lo range. That’s what led me to believe that the control module might still be good.

Flash forward to the next morning. Out of curiosity, while starting my car to warm up; I started the Explorer to see if I had flashing lights again. Lo and behold…..the Hi was back to flashing and I’m back to square one with trying to track the problem down. The transmission has been able to engage in all gears but when you try to put it into 4x4 Lo it will hesitate and the light on the button will flash instead of staying constantly lit. While trying to get it back into Auto or Hi it will hesitate for a bit then eventually shift over.
The windows and dome lights still work and I have checked all the fuses.

My questions:

*Where is the VSS located? Were the two I pulled actually the correct input and output sensors?

*If the 4x4 CM was bad…would one tend to believe it “should” be completely out and not shifting into at times into either 4x4 range? Granted it is electronics and can be finicky…but still. If it was bad I would think it would recreate the same problem over and over again. Not different ones every time upon starting.

*If I DO end up buying a new 4x4CM, do I really have to have a dealer flash the different module for my specific year? I have read some people just “swap and go” with no problems.
I apologize for the length, but I wanted to be as detailed as possible. Thanks all!

 

[Dave8338]

Sounds to me like it is the 4X4 shift motor on the transfer case. They tend to do what you are describing when they start to fail and only do a partial shift of the transfer case, leading to the false neutral you mention.

 

[Viol8R]

Thanks Dave. I will give that a shot.

Just looking for any ideas and thought besides my own.

 

[Viol8R]

I have not had a chance yet to do as Dave suggested and swap out the TC shift motor. The truck has mostly ran with no problems; but on some days with the 4x4 Hi light on dash flashing seemed to run "somewhat" normal. This evening though the 4x4 Lo light on both the button and the dash both lit up and would not come out while doing the standard "push 4x4 Auto button while in reverse or neutral". I tried backing up and all the old "tricks" and still stayed in low. As I did this the light on the 4x4 Lo button began to flash and there was no distinctive sound from the control module as it had done before while working normally. I decided to disconnect the battery for over 20+ minutes. Hooked the battery back up....fired the truck back up and the 4x4 Lo light on the dash and button were illuminated still. I shifted the truck into reverse and pressed the 4x4 Hi button....and lo and behold she shifted. I went through all three (Auto....Hi...and Lo buttons) and all seemed to work properly.

Can the shift motor cause this problem prior to un-hooking the battery then suddenly work after the battery is re-connected? Or.... does this just seem to be isolated to the Control Module? The weird thing to me is that I have never noticed the light on the button itself flashing. Then after reset have it happen again until I press the Hi or Auto buttons.