Hi all,

I know these symptoms have been covered before, but I'm not that experienced with working on vehicles, so please bear with me.

First, some background:

I've got a '98 Expedition that, for the last few years, has not
reliably been able to go into 4WD (high or low). I believe it started
around the time we had the driveshaft replaced (it was out of balance,
got worse over time, 2004). The dealer, in Springfield Missouri,
replaced it and we continued on our cross-country road trip. A day or
two later, I tried to put it in 4WD to drive on a beach and it
wouldn't engage. No noise, no click, no light, no nothing.

So, we took it to another dealer in NY. We told them what had been
done at the Springfield dealer and dropped it off. They called us an
hour later and said the problem was fixed. They claimed it was some
sort of loose electrical connection, where the previous mechanic had
probably used a pair of pliers to yank off the connector. He said the
crimp got damaged, so they crimped it back on and everything worked
again. And, sure enough, it did.

If I remember correctly, he said the problem was under the truck, and
where you would disconnect a harness if you were doing diagnostics.
But it's very possible I may be misremembering that.

Anyway, a few weeks later, no more 4WD. Same deal - turn the switch,
nothing happens.

A few weeks later, it's working fine again. A day or two later, nothing.

Sounds like a loose electrical connection to me, though I've never
seen anything obvious when I've been under there. So, we took it in to
a local (non-dealer) mechanic for some other maintenance and I asked
him to look for anything suspicious to him while he had it on the
lift. He looked for obvious signs like oil dripping onto harnesses,
loose connections, etc. Nothing. (At this point, the 4WD is not
working)

So, we took it in to another dealer here in California. This time,
they say it's the fabled GEM module. They told us about the windshield
leak problem, and claim the GEM module needs replacement. They also
claim we need "output speed sensors" and a new windshield. The
estimate for this work is $1450!

From what I've read here, the GEM modules do cause this sort of problem. What bothers me is that I'm not sure it there was rain involved each time it stopped working, but... corrosion is corrosion. I've also never seen water in the interior.

So, my questions are:

- Does it sound like the GEM to you all?
- If it IS the GEM, is that something I (an inexperienced, though
fairly handy person) can replace myself?
- If I can replace it, is there a HOWTO somewhere? (If not, I'll happily
write one up if someone can walk me through it)
- Is there anything else I should try that perhaps the dealer didn't?
- What is an "output speed sensor" and why would I need to replace them?
- Is it possible to waterproof the GEM module with silicone or something?

Thanks for an insights you all may have. I can't afford to spend
$1400+ on this truck at the moment, but with the rains I could sure
use the 4WD!

 

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Thanks, Tim.

Anyone out there have any thoughts on this problem?