4x4 system check help in Columbia, SC

Hi.

I want to test my electric 4x4 system and am pretty sure my control module isn't working.
I have a 2002 FX4. Is there anyone in the area that would be willing to help me check this out and let me use his / her control module to test everything else on my truck?

Or is anyone willing to part from a functional unit at a reasonable price?

Thanks a lot.
Olivier

Odd way to test system, could end up damaging 2nd module

Do the 4WD lights come on with key on and then go off, thats a bulb test?

When you select 4WD do lights flash or nothing happens?

Check engine fuse box, fuse #13 20amp, powers the shift motor
Cab fuse box #5 15amp powers module


If 4WD lights don't flash when you select 4WD then either fuse is blown or module is bad
If lights flash then shift motor is most likely the problem.

The switch itself could fail but very rare, inside the switch are 3 resistors, one for each selection, 2WD, 4high, 4low
With key on Module sends the switch a fixed voltage, lower return voltage thru a resistor tells module what position the switch is in.

When 4high is selected voltage at module changes and it activates one of TWO relays inside module
The shift motor is a 12volt DC motor like power window motor, so if one wire to motor is a Ground and the other wire is 12volt then motor turns Clockwise, if you Reverse Ground and 12volt on the two wires then motor turns Counter Clockwise, window up window down.

The two relays in the module are Both Grounds when off
Module activates one relay so one wire is now 12volts the other a Ground and motor moves in a specific direction.
Inside the motor housing are 5 contacts, the module can "read" the position of the motor by what contacts are opened and closed, so 2WD, 4high, 4low each have specific contact open/close pattern.
So module "knows" by the pattern what position the motor and transfer case are in at any given time.
So if you were in 4high and selected 4low the module would know to turn motor Counter clockwise to get to 4low, or if you select 2WD it would know to turn motor Clockwise to get to 2WD.

If you were in 2WD and selected 4high, module would power up the motor, if the contacts in the motor didn't change instantly the module would stop power and start flashing 4WD light to tell driver there is a problem

So if there is no flashing 4WD light then most likely the module is the problem or fuses

I think the 4x4 module used was the same on many years and models, wrecking yards would have that info

Tap on shift motor with hammer, lightly, lol, that can unstick the electric motors brushes and get it to work again, although it would need to be rebuilt if that works.

For future reference you should shift in to 4low and back to 2WD once a month, don't have to move the truck, just shift it, that keeps brushes clean and the gear lubed

Ron.

Thanks for the info.
It seemed to me that quite a few people suggested this procedure online.

I don't get any lights on the dash board when I turn the key.
I'll double check the fuses to make sure they're all good.
My guess is that the module is bad and unfortunately there are no compatible ones in the area.

Olivier,

There are 3 good junk yards here in SC that you can check. Search for "LKQ" on Google. They have a yard in Greenville, one in Greer and another in Charleston. You can check vehicle inventory on their website. There is at least one photo of each vehicle. They usually have a few Rangers, mostly 2-wheel drive. But it's worth checking out. Their prices are decent. If you set up an online account, you can have them send text or email notifications when certain vehicles enter the yard. AND... They will be having 40per cent off sale on Thanksgiving.

With no lights at all on your switches, may be it's just a blown fuse or loose wiring connection.

Eric B