I have a 99 Expedition EB, my vehicle has the three position Transfer Case selector switch, A4WD, 4Hi and 4Lo. So it is always in All wheel drive.

what is happening is the system always locks the transfer case into 4Hi when the truck is started, so when I drive on dry pavement the front end winds up and pops (NOT GOOD!). After about 1/2 mile the system disables(errors) and the cluster 4X4 light begins to blink and I am in 2X4 Mode. For testing I have pulled the fuse for the electric switching motor on the transfer case and the 4X4 system is abviously disabled in addition the 4X4 light on the cluster blink. Replacing the switching motor did not fix the problem.

I have pulled the battery cable and waited for 15 minutes to reset the relays. (as per instructed by another exy owner) No effect on syptoms.

I think it is a sensor somewhere that is sensing that it needs to be in 4HI but I am not sure.

What should I check next?
any help would be great!

thanks
loonybin88

 

I would check your hall effect (speed) sensors that are mounted on your transfer case. Chances are one of these is bad. Other possible culprits could be your torque-on-demand relay which is buried under the dash or could even be your GEM module. You may have to take it to your local stealership and have them see what error code comes up. You can check the ohms on the hall effect sensors if you have a multi-meter. Unplug the wire connector at the shift motor that you replaced and measure the resistance between terminals 2 & 6. If you get less than 10,000 ohms, replace the rear sensor. Do the same test for terminals 4 & 8 for the front sensor. Is this a new vehicle for you or have you owned it for awhile and just started experiencing the problem?

 

I would also check the three position switch on the dash ........ to confirm that the contacts are working and the correct signal is being sent to the other components down the line.

99 Navi Guy ..... (74000 miles - 5.4L 32V - 4X4 - 3.73LS - 17 " Wheels - LLS)

 

Thanks for the replies,

I will test the ohms on both sensors, I do fear that it is the relay switch/GEM Module which is a costly repair according to what I am told.

I have owned this vehicle for almost two years now, and other than the starter solenoid going bad (I was surpirsed Ford still uses it!) I haven't had any other problems. It is by far the best vehicle I have ever owned, both for comfort, versitility and room for the kids.


I have already rebuilt the selector switch once but it couldn't hurt to do it again.

thanks
Loonybin88

 

I had to replace just about everything in mine, shift motor was fried, relays were bad and the GEM. The only parts that were not bad were the speed sensors but I replaced them as well. I found a used GEM at a salvage yard for $65 and it worked just fine but you pretty well have to get one for the same year vehicle due to changes in the functions that these control. I believe NAPA is starting to sell aftermarket GEM modules for around $120 so you might check with them. I know my project was a long, frustrating troubleshooting process and expensive as well even though I probably saved $500-$600 by doing it myself. I found the shift motor on ebay for $105 (new) so this was considerably cheaper than the dealer. There's two relays under the dash. I paid around $155 for the pair and found I could have fixed the shift relay for $4.00 in parts but I have desoldering tools etc. If yours is shifting into 4Hi and 4Lo, this relay should be good. You might save yourself a lot of time by spending the $75 or so to get it diagnosed. Sorry for omitting the switch on my first post---you're correct in checking it first.

 

Hey thanks for the update, my system switchs fine into 4HI and 4LO, so I think the relays are good, it just is always stuck in 4HI when starting then kicks out after about 1/2 mile of driving. So I am inclined to think that it is the sensors like you suggested. However I have replace the switching motor (from Ford) at $250.
What exacly does the GEM Module do? this still might be the problem, but I could definitely look for a used one from a slavage yard.

thanks

 

It does sound like your rela

 

Sorry for the incomplete previous post (2 year old wanted to play on the computer). It does sound like your relays are OK and also your GEM--the GEM module controls most of the interior electronics, ie, power windows, lights, mirrors, etc and also all of the 4WD functions. It interprets the signals from the switch, speed sensors, brake pedal position sensor, transmission position sensor etc and activates the shift motor and the transfer case electronic clutch for the awd mode---pretty much the command center for the whole system. It sounds like you can rule this out or at least move it way down the list. Check the ohm readings on your speed sensors and go from there (after verifying that your switch is working correctly). If you pull your switch you can check it easily with an ohm meter--check the resistance between terminals 2 & 3 while rotating the switch through the 3 positions. You should have these values--3700-4100 for 4awd, 1040-1160 for 4HI and between 340-380 for 4LO. Hope this helps.

 

I am going to be testing these suggestions later this week. Where exactly is the Torque-On-Demand Relay located under the dash? is it drivers/passager side, behind air blend box etc......

thanks again

 

The TOD relay and shift relay are a little tough to get to. They are located right on top of the dash, almost above the radio. You have to remove the trim cover around the radio (turn the air vents inward and you can pull the panel straight out by grabbing inside the vent openings) unplug the connector for 4wd switch, remove the upper steering cover trim (4 clips, pull out gently towards you and also put gear selector to 1st gear as this makes access easier), pull out the headlight switch (you will see a small notch on the bottom that you can slip a screwdriver or similar tool into to pry out from the bottom--best to wrap a little tape on the blade to keep from damaging the trim) and disconnect the wires for it. Remove the instrument cluster finsh panel (6 screws) and disconnect the wires for the rear window defrost button (pedal adjust button also, if yours has this option). If memory serves me, you should now be able to see all of the screws (5) to get the upper dash/instrument cluster panel off and reveal the relays. I might have missed something but you should be able to see most of the hex screws as you go.

 

I checked the ohms at the selector switch all was good, i checked the ohms at both speed sensors (hall effect) I got an open on both sensors. do these sensors have any thing to due with the shifting of the trans or just the autoclutch/switching motor for the transfer case?

also, my bro has an 98 expedition with the four position selector switch do you know what the ohms should read for his vehicle?
also could a faulty O2 sensors that gives a Check Engine Code lock out the 4wheel system?
He thinks that when his 4wheel systems fails to switch into position, he pulls the neg. battery terminal to reset, and the 4wheel system works fine afterwards.

thanks

 

The speed sensors and the TOD relay are independent of the shift motor and combined with the GEM, control the electronic clutch in the transfer case. I'm not sure on your brothers 98 as my hands-on experience has been with my previous '99 expy and the present '00. I know his 98 has a vacuum switch for the front differential which the 99-00 do not have. I don't think that the faulty O2 sensors should have any effect on the 4WD and would probably check elsewhere. Maybe someone else with 97-98 expertise could add some input on this issue.

 

At the risk of stealing this thread ....
Mtitech,
You have a very good understanding of how the Expedition AWD system works, in my case I have an 01 AWD XLT (this vehicle is "gift" from my BIL to my wife) that we use for towing. Unfortunately the transmission has failed (my 3rd Ford transmission failure out of 3 vehicles) and I am in the middle of pulling it to have it rebuilt. As part of this repair, I am sort of half considering removing the AWD system (transfer case, front diff and drive axles) and running it as a 2WD only. I understand that a different transmission (tail-housing) and drive shaft would be required, which seem simple enough considering most is removed to get at the existing transmission, but I am more concerned with the electronics. Will the "GEM" and engine management electronics be "OK" with the transfer case connections left disconnected? (All vacuum lines plugged.)
Thanks in advance.

 

Sounds like quite a project and sorry to hear you've had such bad luck with the tranny's. Do you have the 5.4 in the 01 with the 4R100 tranny? You will probably be OK leaving the existing GEM installed but you will have the 4 X 4 dash light blinking at you most of the time. You might check with your dealer and see if they can flash it to the 2WD specifications or locate a good used one from a salvage yard---generally go for around $60 used. Be sure to look for one for the same year of vehicle as these do vary for the functions that they control. If you have the $$$ in your budget, you may want to buy a new one. Keep us posted on your progress.

 

Mtitech -- Thanks for the reply.
You are correct, the trans removal on the AWD Expedition is a "big" deal.
I have the 5.4 engine with the 4R100 trans in the 01 Expedition. The mileage is 45K. It has the factory tow package with the optional 3.31 gears. It really needs steeper gears for serious towing. I use it for towing a horse trailer (4000 lbs max) and also a car (on a tow dolly), both are within the allowable factory specs. My other Ford trans failures were in Explorers, one in a 94 (failed at 100k miles) and one in a 00 (failed at 56k (reverse pressure modulator). In both cases, I had the original units rebuilt with good results. I still own the 00, it now has 85k miles. I sold the 94 with 170k miles. Unfortunately with these trans failures, even though I am a big fan of the Ford SUVs, per the other decision maker in the family -- there will never be another one in my driveway. I guess I am looking at that the Nissan Titan or Pathfinder when the time comes for a new vehicle.
I will keep you posted on what I end up doing.