2000 f150 5.4 4x4. I managed to pull codes p1812 p1815 from the gem I forget what the first one is but the second one says 4x4 short to ground or something similar. It is electronic shift on the fly. You can hear the relay click behind the dash and when you select each setting, 2H 4H and 4L. The gem also reads properly. When I hook up the genesis scanner, pretty much nothing works, even the winshield wipers. I am able to get 2H and 4H but no 4L. The resistance on the switch on the dash is right in spec and the shift motor on the t case is brand new. I don't know where to go from here. The brake switch also works, my lights do come and the neutral safety switch also works i am able to start it in neural.

 

Pull the motor, then re-install it again. I don't know why, just know that it worked for a few users.

I wouldn't even bother posting that if it just worked for one guy, - but it did work for two others in the past. I guess that makes it credible and worth a try before spending any cash to fix.

 

Just did it twice testing both times. First time was in 2wd and tried to go to 4 low and next time I left it in 4 low and it was set right at 4 high on the t case itself....

 

P1812 Transmission 4-Wheel Drive Mode Select Circuit Failure
P1815 Transmission 4-Wheel Drive Mode Select Short Circuit To Ground


I believe the Red wire is GEM ground correct ? Is that right, I did fool with that once ? I guess I could look it up, but what would help that you haven't checked ?

 

Yea, it should go right into low. Did you try switching from 4wd high to 2wd, then give it a roll , -forward and reverse, stop, then 4wd low ?

Yea, mine will find low and stay there as long as the wheels aren't turning.

 

I've tried nearly everything and right now I have got the GEM module out and checking resistance i have the pin outs here from all data and I get zero resistance in circuit 682, a dark blue wire. Now my problem is that I have no idea how to read the wiring schematic.

it goes from the multifunction switch T's off and goes to signal return and the other end goes around and comes back to the 4x4 switch that is on my dash

 

its wierd I have no problems with the multifunction switch (switch on the steering column that controls wipers, signals etc) except when that scanner is hooked up to it.

 

Can you pinpoint the 4wd low ground wire? I imagine it's shared, -so a schematic should show the splice point somewhere, - know what I'm sayin ?

I think it's a ground. I know there's two in cab behind the kick panels, but I'm not sure if their GEM or not. I'd have to find a diagram myself lol.

 

I have the 2000 Service DVD if anything off that would help.

 

Did you by chance mess around with the 4wd actuator lines?

If so, Ford has those backwards on all their diagrams, - every damn one. If you followed those, your lines are most likely backwards.

 

There is one behind the passenger kick panel and I found that one. I believe there 2 grounds behind the drivers kick panel and I found them as well. I never traced them back very far.

 

I did mess with the actuator lines before Christmas when I was diagnosing why the front hubs weren't engaging, that was a vacuum disconnect solenoid, the 2wd wasn't disconnecting thats all better and I had 4 low then. But I don't have problems with the front hubs.

 

I took a picture of the schematic I am dealing with right now, it is the highlighted one I am dealing with right now.

 

The ESOF'S, more times than not, it ends up being the GEM. The F150's have that windshield leak that you can't see, but that did corroded that module in particular. Very hard to see any evidence of this as well.

I've heard you can hit the GEM with WD40 and that worked sometimes lol. Not sure I'd try that one, but I've heard it before, more than once.

Good Luck Gotts

 

If it ends up being the gem I'm just putting it back together till it gets worse. If I get my tuner to shut off the pats could I replace the gem with a new/ good used one?

I will not take it to the dealer unless ABSOLUTELY necessary. I hate it when others work on my truck