Hey folks, its been awhile! (My truck has been so good to me) Up until today!

Well I was driving down the road and all the sudden clicking in the dash faster click click click click click and the 4x4hi light is going on and off and I can feel the 4x4 engaging (this is around 55MPH) So I make my way back home after messing with the ESOF switch on the dash and it eventually behaves, kicks into 2wd and I get home. I checked everything, all vac lines, took apart connector on transfer case motor, blew out with compressed air, snapped bakc together all nice and dry.

It will work normally in the driveway but for some reason up to speed on highway (vibration issue?) It randomly shifts into 4x4 hi when it feels like it.

Mechanic friend told me mostly likely either transfer case motor (looks rusty and possibly cracked on housing were wires go in) or its the dash switch ****. I asked him about GEM (where the heck is that) and/or vac lines, he said if it engages normally sometimes its not VAC its def. electrical, he said GEM is only culprit if you have a water issue with leaking windshield/etc.

Anyone experienced this "phantom" 4x4 shifting?

Thanks for any input!

 

Hi guys, well I went ahead and put on a new transfer case shift motor. The OEM one was super rusty and didn't look good.

Put the new one on with some silicone around the mounting plate for sealing and di-electric greased the heck out of the plug connector. (I figured out how to unlock the pins so the brown wire running the transmission could be inserted into its new plug hole on the new motor plug.) Anyways, got it all bolted up nice and tight and before I put the new one on I took a pair of vise grips with a thick towel and gently moved the shift rod on the transfer case back a forth a few times from 2h to 4h just to make sure it moved smoothly which it did.

Had the battery unhooked the entire time I did this so the computer would reset. Hooked everything back up and started truck after making sure the 4wd dash **** was in 2H. I heard a bunch of relays clicking under the dash on start up that sound like they do when you switch to 4wd normally, then they stopped and the truck idled down.

Took the first chance and switched to 4H, fine, very smooth sound almost inaudible and switch to 4L, normal clunk as it always did. Tested both ranges, everything seemed good so I took it out on the highway.

No dreaded phantom shifting on its own so I think i may have got it. Perhaps it was also a computer confusion issue as well? Maybe resetting the computer did it some good as well? Is it possible the computer gets corrupted from bad connections on the transfer motor and doesn't know where to shift?

Cheers!

 

im glad to here you got your problem fixed. a freind of mine had this same issue with his 99 f150 and that worked for him to.

 

I think it was a real good idea to replace this, check out the internals of the old switch. The rotary contact plate looks shorted and burnt in a few places. Also the contact fingers looks dirty (i know the contact grease is colored a bit). Anyways whatcha all think?

 

As a point of info; the computer (pcm) does not have anything to do wth controlling the 4x4 shift into and out functions.
The GEM module conducts all the functions and reporting on the dash once the selector switch is operated.
The dash switch position, the DTR and brake pedal signals are used for the selected functions.
A wire fault, contacts or GEM fault can cause malfunctions.
The PCM controls the shift points as normal in 4H and the PCM still controls the shift points in 4L but the shift points are changed due to the large increase in gear change that takes place in the overall gearing.
4L demands you place the shift in neutral and apply the brake before the GEM will proceed to allow 4L function because of the large down gearing that takes place would cause big issues for the driver, passenger and drive train if it were allowed to take place and any speed much above 5 mph.

 

HI Bluegrass, so basically the erractic shifting I was experiencing before was a mis-communication between either the dash switch/GEM/transfer case motor position sensor correct? I am assuming it was either the motor or the dash **** malfunction as those are the only two of the system that directly feed to the GEM for positioning it in either 2 or 4wd.

The contacts in my pictures look like they've seen better days so hopefully that was the problem. 4wd works excellent now, not as noisy when engaging either.

I did peek at the GEM (up under dash near steering column?) and it appeared like new and not wet (had alot of rain/snow lately so I figured it would be prime time to check it.)

 

You got it right. Not the PCM but something else.
The dash switch only "requests" the function.
Once requested the GEM causes the tranfer case motor to run to position, operates a firewall relay and reports back to the GEM the actions have completed, then the GEM lights the dash lamp per the requested function.
Isn't 'logic' wonderfull?
Good luck.

 

Hey Bluegrass

Ok, that makes it clearer. Not really complicated but theres ALOT of "talking" happening when you flip the dash switch.

So basically, dash switched to 4h talks to GEM, GEM then talks to transfer motor to switch to 4h, transfer motor activates and completes switch, then talks back to GEM, GEM then lights dash indicator lamps.

Have I got it?

More importantly do you think that replacing the transfer shift motor was a good move or should I have replaced the dash switch instead? (Still the OEM switch) regarding my inital problem and experience? Both were equally expensive ($95)

 

Test and diagnostics are always the best way to be sure you spend as little as needed and have to do the least work.
Easy to remove the tranfer motor and try to access 4H to see what it does.
When the tranfer motor goes to end of it's rotation , it is supposed to send a return signal to the GEM as operation complete.
When the firewall relay operates it also sends a signal back to the GEM to tell it the front has attempted to function the vacuum motor and engage the front drive..
Anything that's missing is a problem like an open in a cable, motor contacts, vacuum line, relay etc..

 

Witnessed this exact problem with an '03. Problem started after windshield replacement. A disconnect of the negative terminal for a few mintues, and reconnect, solved the problem. Has not re-occured since.

 

Well guys I lied......problem is back. I tried pulling the dash switch (just unplugged it) and the truck STILL shifted by itself into 4x4 high. Reset truck, disconnected battery for 1/2hr with lights left on, etc to drain system. Nope, still doing it. I have a brand new transfer case shift motor, so its clearly not the problem.

Does this topic pertain to my truck or is this for manual systems only? https://www.f150online.com/forums/tr...-problems.html

I'm just wondering how the heck can it shift with the dash **** disconnected?!!!?

 

THE GEM may be causing your erratic shifts. When you unplugged the switch the resistance became infinite and the GEM should see that as a request for 4x2. If it shifts after that the GEM is causing it or the transfer case shift relay is malfunctioning. Odds are the GEM has had water intrusion and is causing the problem.

 

JMC, thanks for replying! I should probably try a relay first as it is cheapest! Unplugging the switch did shift to 4x4. Did I mention this seems to be more of a problem with increasing vibrations? (hoping its the relay!)

Is there any way of saving the GEM if it is water related? Some days this goes away.

 

There is no way of really telling if the inside of the GEM is wet unless you open it up. Sometimes just cleaning the contacts of the corrosion and applying di-electric grease saves the day. The 4x4 relay could also be the culprit ( cheaper than a GEM). It is up under the dash between the steering wheel and the radio. Try that first.

 

Hey JMC< wheres the 4x4 relay exactly? How can I access it? I took the GEM all out and apart gently, everything looked great. Di-electric greased all connections, lightly. Blew out with compressed air, and electrical cleaner, ensured all was dry. I have pics which will be up later.

Is this 4x4 relay a part I could get at NAPA?

THANKS!!!!