Earlier this winter I was driving about 50 mph and heard an intermittent grinding noise, on and off a few times then I didn't hear it any more. Later that day it started again, but continued grinding so I pulled off the road into a parking lot. I noticed that the 4WD Low light was on then, and in driving around the lot, confirmed I was in low based on how it drove/handled/turned yadda yadda. The switch was in 2WD but I was clearly in 4 Low. I was unable to get it out of 4 Low so ended up having it towed to my mechanic. He initially advised it was the Transfer Case Motor, but then when I went to pick it up, he advised he had changed the selector switch.
Couple months later, it does it again. I left it overnight and in the morning was magically out of 4 Low.
The other day, drove a couple hours, parked and went into a store for about half an hour, came out, started her up and lo and behold, I was in 4 Low, light was on, as has been the past, and it was clearly in 4 Low. Switch of course was still in 2WD.

I tried switching into and out of 4 High, 4 Low (yes in neutral, brake on etc) and tried backing up in reverse a number of times. The selector switch did nothing at all. I ended up driving slowly across the street to my hotel, and then in their lot, backed up for quite some distance. Put her in drive to park, and magically, I was out of 4 Low.

It is switching itself into 4 Low while the selector switch is in 2WD, and it doesn't matter if power is on, or off.

I'm suspecting either the Transfer Case Motor, but leaning more towards the Transfer Case Control Module. My thoughts are since the power is off, there's got to be some kind of electrical glitch, hence my thoughts towards the TCCM.

Any thoughts on this odd bit of magic?

 

We assume Ford Ranger and a 4x4

Year and engine?

Depending on the year shift module is possible cause, but in most years no not possible

4Low has a top speed of 30mph, and thats flat out in Overdrive, lol, so 4low right???
i.e. you are not driving home in 4low, unless you live in Hemet Calif, home to the "Bluehairs", top speed 25mph.

The 4low light on the dash is activated by the transfer case shift motors contact wheel.
Inside the shift motor is a wheel with 5 contacts, as the motor turns the transfer case the wheel turns and contacts are made and broken until the correct pattern is seen by controller then it shuts off power to the motor

Pictures here of shift motor and contact wheel: https://www.explorerforum.com/forums...-motor.123542/

These motors are the same regardless of the year.

Post your year and engine size and we can get more specific

 

2004 Ranger FX4 4WD

V6 4.0L

"4Low has a top speed of 30mph, and thats flat out in Overdrive, lol, so 4low right???
i.e. you are not driving home in 4low, unless you live in Hemet Calif, home to the "Bluehairs", top speed 25mph." Not sure I understand this. The first occurrence was while driving, approx 50mph and in 2WD. This is when my mechanic replaced the dash mounted selector switch. 2nd occurrence happened 2-3 months later, I had switched into 4 Low to help tow my girls truck out of the snow bank, and it would not shift out of low, no matter what I tried. Let it sit overnight and in the morning, it was no longer in 4 Low, magic! 3rd occurrence happened while I was inside Bass Pro Shops. I know, she was upset that I was spending money on the boat instead of her, so she once again magically switched into 4 Low. lol I had just drove a couple hrs on the freeway, and it was hot and muggy as hell, so don't know if that factored into things.

And yes, I topped out about 25-30 driving to the hotel (about a mile), flashers on, trying to stay our of every-bodies way. Hated to do that, but I wasn't really in the mood, and I had a cooler of beer in the bed.

 

2004 was the first year Ranger went full digital, i.e. Smart Junction box and digital dash

When you turn on the key the computer and 4x4 module boot up
The 4x4 selector switch is just 3 different resistors, 4x4 module sends it 12volts, and gets back a LOWER voltage, depending on which resistor is selected, there will be 3 possible voltages, each represents a "selection", 2WD, 4high and 4low
It then checks shift motor's contact pattern for its current position.
If return voltage from dash switch doesn't match contacts pattern then 4x4 module changes the shift motor to match selection on dash switch.
This all happens in under 5 seconds from key on
So if it was in 4low when shut off and you tried shifting it to 2WD but it didn't work at that time, and left switch in 2WD position, then at next startup it would shift to 2WD, no magic, lol.

Dash selector switch is the least likely to fail in these systems, so not sure why a shop would go there first?
But if shift motor was activating without drivers input(change in switch) then that would be something to test, pretty easy to test for 3 different OHM readings

Good read here on where 4x4 module is located: https://www.ranger-forums.com/4-0l-o...module-140263/

Shift motor is just a 12v motor like a power window motor, it has the contact wheel but that is just an analog system, so shift motor can't change on its own, there is no voltage present until 4x4 module sends it out.
If contacts are not working 4WD lights will flash, that's an indicator of blown shift motor fuse or failed shift motor

So you are down to 4x4 module issue as most likely cause of this random shifting of transfer case.
It is possible the wiring from the dash switch is the problem, i.e. voltage change is causing 4x4 module to think 4low is selected
If you pull out the radio to get to 4x4 module I would turn on the key and select a few 4x4 positions and then back to 2WD then try wiggling the 4x4 module wires to see if you can get a random shift to 4low, indicating a wiring problem not module problem
I don't know the actual Return voltages the 4x4 module expects for each selection

2004 4WD wiring diagram below

 

Thank you for the information. I was pretty much convinced that it was an electrical issue, as is my son, who is the wrench in the family.

And as much as I was hoping that my control module was on the side of the pass. floor, I had already read the thread about it being located behind the radio. Now I just have to get the ford radio removal tool thingy and a new module.

I imagine they changed the selector switch out because it wasn't doing anything? They initially suspected the motor, but then came back to the switch.

As I don't really need 4WD right now, and are starting to build a house, I really can't afford to spend the money on the module right now. What do you think about disconnecting the harness to the motor (protecting the ends) to prevent inadvertent shifts to 4 Low until I can afford to get the module?

 

You don't need the radio removal tool. It will be just as easy to remove the whole plastic surround. It's just a few screws.

 

Yes, or pull the fuse for the 4x4 module, in my Power diagram it shows fuse #27(20amp) in engine fuse box is just for the 4x4 module, that should disable the 4x4 control

 

Thank you Caleb

 

Thats a better idea, thank you