4hi 4lo and A4WD randomly coming on?!?! *pulls hair out*

[l3l4k0ut]

ok guys..i have a 98 EB expy. 229000 mi. almost cherry! cept this...TODAY it started doing this...EVERY light pertaining to 4wd will illuminate (A4WD, 4HI 4LO, LOW RANGE) while driving, relays click and WHILE DRIVING rpms will bog down because it literally DID just shift into 4LO. concerning, no? now, i am mechanically inclined, i was ASE certified until about 6 yrs ago but since then i just do my own vehicles. but this one has me scratching my dome. im *somewhat* familiar with 4wd on these trucks, but not a lot. to save my transfer case n other 4wd components i tried pulling fuse 23 in CJB and fuse 17 in BJB. from my understanding, and according to identifix, fuse 17 in the power distro box controls the t-case in its entirety, correct? or am i misunderstanding it? the reason i ask is because even with both those fuses pulled she STILL does it... think ill just disconnect the connector @ the t-case until i figure this out. and PLEASE don't tell me this is the dreaded GEM problem...wouldnt i have more problems if that was the case though?

 

[bedrck46]

Ok I won't tell you that it could be a GEM issue I have attached some prints for you to review. As you can see from those prints almost every thing goes thru the GEM. After see these wiring diagrams you may want to tell yourself that it could be GEM related. These prints are from the Ford service manual for a 97 expedition the prints for a 98 are identical.

 

[bedrck46]

there also could be a problem with the brake switch. I know your going to say your brake lights work just fine. That brake switch also serves other items, it is a multi circuit switch.

 

[l3l4k0ut]

thx bedrck46..man i kinda figured it could be i jus dont wanan go thru the hassle of pulling it all out. i DO have a windshield leak...only place with rust is near the driver's side on the roof by windshield. so...yea i kinda figured it was, just telling myself it wasnt. i dont have the funds to get that fixed, so no use in replacing GEM at this point to only have it happen again shortly. so i figure best way to prevent this from messing up my t-case and all is by disconnecting the electrical connector at the t-case. anything else i should do for now until i can get a proper fix?

 

[bedrck46]

although I haven't been on the forum as long as others I have noticed that a lot of the times that the gem gets blamed for being the problem I have noticed it is water in the fuse block that seems to cause more problems then the gem.

The fuse block can be dried out if it is a case of water. The gem nodule is easy to take apart and inspect the printed circuit board for any signs of corrosion bad solder joints or burn marks.

My only advice in removing the fuse box/gem module would be to disconnect the two large connectors on the back of the fuse box and also remove as much of the dash that is needed to get the assembly out Just be careful as a little bit of prying may be needed use a little force but don't over do it. Also use a flashlight and mirror to see behing the assembly.

Once out of the expy shake and turn the fuse box to see if any water is in it and use a hair drier to dry it out although some have placed it in an oven at a low temp to aid in drying.

 

[l3l4k0ut]

pulled the fuse block/GEM out. took cover off GEM (which had a clear plastic cover over it made to fit over GEM...previous GEM issues?)...printed board looks fine, no burns, all green,...fuse block seems dry. could it still be this or something else? btw it didnt start this morning either. batt is NEW n wasn't drained, tested fine, terminals tight. clicked once, but absolutely no add'l batt draw, lights didnt dim, no movement of voltage gauge. tried 4 more times...started...thats when i decided to do this after i finished running some errands using my other vehicle....any suggestions? btw...this isnt easy with one arm...dislocated shoulder w/police testing so i hope u dont tell me i gotta take more apart lol...

 

[fryguy]

Did you ever figure this out? Mine started doing this today after the shop changed plugs and a fuel filter. A little disappointed with the shop. Hoping they fix it. Sitting in the shop overnight.