All,

First let me start off by stating I searched the archives for info on my issue, and got a little bit of info to troubleshoot but still need some help.

I have a 1998 Expedition 4x4 with electonic shift on the fly. I have 2W AWD 4WH and 4WL on the rotary dial on the dash. During start up, all of the lights in the dash for the respective mode light up, so I know the lights work. Rotating the rotary dial to try and get to AWD, 4WH OR 4wl, I get no lights in the dash and no response from any of the systems.

I pulled the dial from the dash and used my volt/ohm meter to test it, and it appears fine, and I also tested for power from the harness, and all seems fine. I also went to the two solenoids on the Pax side firewall, and I have Vacuum with the bottom two lines, Blk & Wht line. Not sure how to test to see if I can get vacuum to the top two, Pink and Light Blue? to verify if the solenoids are bad. Any suggestions on how to fully test these suckers?

I also got under the vehicle to the front axle and looked at the vacuum shift motor diaphram and used my mit-e-vac to pull down vacuum on the inner hose connection. It held firm at 10. I also moved the rod connected to the shift fork, and the fork itself, and it moves about 1/2" in and out. Not sure how far I should be able to move it and not sure if I should have tested the outer vacuum connection as my Haynes manual didn't state to test there.

I disconnected the wiring harness from the Transfer case shift motor, it's in great shape, and reconnected it, just in case of poor contact. No luck. After checking each of these items, I am still back to ground zero again. No lights reflect in the dash when rotating the 4x4 dial and no system change to the action of the 4X4 operation.

Hopefully I have outlined enough here that someone will be able to point me in the right direction.

Dave

 

not very experienced in this field but im gonna give a crack at it.

it really sounds like an electrical problem to me. double check fuses and all leads that can be found. probably will end up being a vacuum problem though.

 

I have checked the fuses under the dash and under the hood, all are good. Any other suggestions?

 

Indeed, it sounds like an electrical gremlin... I suspect that either the GEM isn't getting the correct signal from the switch, or the GEM itself is bad. If it's not even trying to lock the t-case, it's likely not getting the signal to lock in the first place. If it was getting the signal but failing to lock, odds are the light would start blinking...

-Joe

 

Ok, I gave in and bought a tranfer case motor from Oreilly's and replaced mine. Figured for 65.00 it was worth doing, since its a 1998 I fugured I can't go wrong replacing it, plus it rules out one item as suspect.

With the new Transfer Case Motor (TCM) installed, when I rotate the 4x4 dial to AWD, the light on the dash now goes AWD and I can hear the Vacuum solenoid on the firewall click. So far so good. I need to go out and drive it somewhere where I can get the rear wheels to slip to verify the front wheels are indeed engaging in AWD. That's to come this evening.

So I figured I would drive a bit around the block and try to dial it to 4WH. No luck. Dial to 4WH light stays on AWD. Stopping, putting it in neutral and dialing to 4WL I get nothing. Light on the dash stays on AWD.

I now at least have corrected one issue with replacing the TCM. I now need to start hunting for the other pieces of the puzzle.

Any suggestions?

 

While driving straight ahead on dry pavement, there will not be a discernible difference between A4WD and 4high (Automatic 4 Wheel Drive, not All Wheel Drive... There's a huge difference). The only difference between the two is that the transfer case locks in at 100% duty cycle in 4high.

Now, as for why it won't shift to 4low, a couple of things come to mind: Was your foot on the brakes? You must be stopped, in neutral, with your foot on the brakes before it'll shift into or out of 4low. If it's getting the signal for A4wd and 4high, then we know it's getting *some* signal through the switch. Have you checked the resistances through the switch yet? The switch itself could be bad.

Without being able to monitor the GEM PIDs (which are the inputs and outputs), there's no way to know exactly what the GEM is seeing or why it's not making the shift. IMHO, the shift motor had absolutely nothing to do with the problem. The fact that 4high and 4auto work now does nothing to confirm the shift motor as the culprit in the first place. Transfer case lockup is not handled by the shift motor. The TCS motor on your transfer case is solely responsible for range selection. Lockup is handled by the transfer case clutch coil which is controlled by the Torque On Demand relay and the GEM (depending on the mode). The signal to lock the case doesn't pass through the TCS motor at all. If the system had detected a fault with the encoder on that old motor, it should have stored a code and flashed the lights.

It's a guessing game at best at this point...

 

I must have misdirected you somewhere. The A4WD light is the only light that comes on. I do not get any other lights when dialing in the 4HI or 4LO.

In fact, once the A4WD light comes on, when I move the dial to 4HI or 4LO, the Dash Light still stays in A4WD indication and I never get the 4x4, 4LO dash lights to indicate. I went out to some loose gravel to test to see if A4WD was actually engaging when the rear wheels slipped, and it seems that phase may be working correctly.

Yes, for the 4LO test, I did have the truck in neutral with the brake pedal depressed fully, and still nothing. When I dial to 4LO, the A4WD light remains on and it does not cycle to the correct indication, nor is the vehicle locking up in the correct mode, 4x4 or 4LO.

Any suggestions what to test next?

 

It could be a couple of things... The most likely candidates in my book are the switch or the GEM failing to get a proper input. Without being able to monitor the PIDs, it's a guessing game at best.

You mentioned that you tested the switch already... Did you check the resistances through the switch in the four positions, or did you just check for continuity through the switch?

My best guess is that it's a switch or an input issue... If it engages 4auto, the only difference between that and 4high is the 100% duty cycle used to lock the case. That's what's making me think it's the switch, but again, that's just a semi-educated guess... Without knowing what they system is seeing, it's just a guess...

-Joe

 

Ok, thanks. I will go purchase a new switch and install it. At least that will eliminate one more piece of the puzzle. I will update this thread when that's done.

Thanks for the feedback thus far.

Dave

 

Huh? I didn't say the switch was bad... If you have a multimeter, 5 minutes with the meter in hand will tell us if it's good or not... Check the variable resistance between the two wires that aren't for the illumination (I forget which two pins they are... they're the ones that'll cause the resistance to change in the four different positions)

-Joe

 

Joe,

Before testing the rotary switch, I figured I would try the ol' reset by disconnecting the Negative battery cable for 5 minutes. Low and behold it worked.

Now when switching from A4WD to 4H I now get the 4X4 light to illuminate and I can tell it locks up correctly. I can also select 4L, tranny in neutral and brake pressed, and I get the 4 Wheel Low light and I can verify lockup with this too.

Hopefully my issue and resolution can help someone else with a transfer case problem.

Thanks for all your suggestions.

Dave

 

I having the same issues, how much does a new Gem cost, and what exactly is it.