I have used Chilton and Haynes and after buying Mitchel I would never go back. Never used Helm. C281 A and C281B are the module connectors. C284 is the connector to Mode Select Switch (2WD...4WD high...4 WD high). So in this test the module is connected, the key is on and I am testing voltage between terminal 3 on the MSS connector and ground. Obviously the MSS is disconnected for access to the connector. I have done the other P series tests that include checking for short to ground and short to 12 volts and all is good. I have the module out and I may hook it up to a power supply. If I put 12 volts in and check the output on the appropriate pin on the module if it is more than 5 volts the problem can only be in the module. I also did most of the K series of tests which check circuitry between the battery junction box and the module. I bench tested the relays. The one K series test I have not done is a disconnect of the transfer case motor. But so far the only test I see a failure on is that reference voltage test.
The most likely solution is remove the transfer case shift motor, manually shift it to 2WD and then fab up something to lock it there. Of course I might win the lottery tonight and just buy a new truck.

Thanks again Y2KW57. Always appreciated.

 

What was the original issue that brought you to this point?

Is the transfer case stuck in 4LO?

 

It is stuck in 4 WD high. It will not shift out of that position electrically and I have not tried removing the shifter motor to see if it will move manually. I had driven a few miles, put it in reverse and backed up a bit. When I went to pull forward I noticed the 4WD High light on and the MSS switch was still in 2WD. I did not touch the MSS switch. It shifted into 4WD High all by itself. When I got home I jacked the vehicle up and tried rotating tires and the hubs were locked. I started the engine, jumpered the vacuum solenoid and got the hubs to release. I had someone drive the truck a few feet while I observed the front drive shaft. It was turning. I jacked the vehicle up and checked the hubs and they were still disengaged. So the transfer case was being driven by the tranny. So the module controls the shifter motor relays from what I see on the wiring diagrams. Something happened in the module to tell it to shift to 4WD.
One of the tests I should mention is the resistance check on the MSS. The three resistance values are all within specs. A failure there might cause the shifter motor to operate.

Anyway it might be hard to believe that I did not touch that MSS switch but I didn't. It really did this all by itself.

If you come up with a possible cause pass it along.

Thanks

 

Since you've proven your capability to force a divorce of hub actuation from transfer case actuation, have you tried just playing with the switch to attempt to "shift" the transfer case into the position it already appears to be in, and then from there switch to a different position, etc? Sometimes encoder motor sensors lose frame of reference, and get lost so to speak, but a few switch cycles can sometimes set them straight again.

I'll give you an example with GM products, since Ford is perfect and cannot possibly have any flaws.....

The GMT800 platform used encoder motors to move blend doors for their automatic temperature control HVAC system. Sometimes, the tiny motors lost their way, and couldn't find home. Vehicle operators would soon realize this when hellish heat was pouring out of the dash vent registers, even though the temperature setting was turned all the way down to the coldest setting at 60 degrees. A logical and ultimate fix is to replace the encoder motor, but to do so in that vehicle platform requires removing the entire dash (per GM procedure... but a few techs learned some shady shortcuts as this happened quite often.)

But what happens if one is on a trip, and doesn't have time to stop for several days down in repairs? A solution turned out to be quite simple, albeit counterintuitive... turn the temperature control to 90 degrees... the hottest setting available. The change in command causes the blend door to move, and once it moves a few times, it has cycled enough to find its way home again.

That's the mysticism behind the movement. The actual mechanics behind what is happening has to do with the encapsulated grease used inside of the encoder motor mechanism, which over time can harden and thus inhibit movement, especially after the vehicle has been sitting for a good long while. The mechanism fails to move, even though the sensor has commanded and sensed that the motor has moved. Further operations eventually can get them synced up again.

As you have probably already read in the Owner's Manual, or already know from experience, if you do play with the transfer case shifting dial in order to excercise the shifting commands in the hopes of getting things back in sync, be certain to always have the transmission in NEUTRAL (not Park) when attempting to move into or out of 4WD. A lot of folks think that shifting the transfer case in Park is "safer", but being in Park resists the geartrain's ability to move and complete the drivetrain shift. With a manual shift lever on the floor, one can feel this resistance through the lever. But with an electronic shift motor, once can't really feel what the electric shift motor is struggling against. Always shift into or out of 4WD with the transmission in neutral, and allow the truck to roll a bit as it makes the shift.

This isn't to say that any of the foregoing will help resolve your case, but it seemed like it might be worth a try to back it up a bit, literally and figuratively speaking, to see if the original concern can be worked around via simpler means before chasing down every CoPart in the country for unobtainium.

 

I have tried turning the 4WD switch while sitting but I was in Park not neutral. I tried changing the switch while moving very slowly in forward and reverse and with the hubs locked and unlocked. The light stays on saying 4WD High. I will try using neutral today. I am a big believer in try the simple stuff first. Getting it out of 4WD will be great and I will simply pull the shift motor relays so it cannot re-engage. I will carry out a few more pinpoint tests today but I keep going back to the fact that it engaged on its own and that 10.8 volts where it should be 5. A cheap and simple solution is my first choice.

Thanks again Y2KW57