Four wheel drive works after computer reset, then nothing.

[toms89]

I can even remember what I searched for, I know it was about the issue, ill search and find the link, Also I think that was for 97 - 2002

I can believe it but the info is inaccurate. The following is quoted from wikipedia.

Model year changes

1998

No major cosmetic or mechanical changes. A new exterior color was added, Wedgewood blue.


1999–2002 cosmetic facelift

1999

For the 1999 model year, the Expedition received a facelift very similar to that of the 1999 Ford F-150. Included in the update was a new front grille which now dropped lower in the center, grille work (that contained the Ford oval badge), as well as an all-new front bumper that now incorporated the fog lamps into the lower valance and larger center air intake. Both the 4.6 liter and 5.4 liter V8 engines received updates including more power and torque. The Two High mode for automatic ControlTrac four-wheel drive equipped Expeditions was dropped leaving only Auto, Four High (lock) and Four Low (lock) modes. The dashboard also received an updated radio and A.C.

2000

Available features on 2000 model Expeditions were expanded to include a hidden......

It appears to be 1999-2002 models that dropped the 2wd setting and center axle disconnect but speculating here. Thats also why there is so much interest in the "brown wire mod" by these particular years. But this only keeps the transfer case from engaging the clutch applying power to the front drivetrain. Does not keep the front drivetrain from spinning while the vehicle is moving.

 

[Tacsat117]

I agree hat I have a vacume leak and that said leak is causing the codes. What I'm really concerned about is why an ecu reset will allow me to shift into four wheel drive for a day or two then stop working. It's not like an ecu reset recharges the vacum line, right? So what in the path would stop working over time, but work just fine after a reset? The truck runs pretty well and I'd love to keep it. I'm hoping this will be an easy fix so I can keep on trucking!

 

[toms89]

I agree hat I have a vacume leak and that said leak is causing the codes. What I'm really concerned about is why an ecu reset will allow me to shift into four wheel drive for a day or two then stop working. It's not like an ecu reset recharges the vacum line, right? So what in the path would stop working over time, but work just fine after a reset? The truck runs pretty well and I'd love to keep it. I'm hoping this will be an easy fix so I can keep on trucking!

Are you speaking about 4 hi, 4 low or auto 4wd is not working? Where/when are you shifting into 4wd?? How do you know its not working? Just trying to get a bit more detail on exactly what it is or is not doing. Does your expy have a 2wd selection?

 

[Tacsat117]

My truck has an "a4WD", 4h, and 4l switch. After pulling the battery cable when I turn the switch from a4WD to 4h I can hear the relays switching then the vehicle goes into 4wd and the dash indicator shows four wheel drive. After a day or two nothing at all happens.

 

[toms89]

My truck has an "a4WD", 4h, and 4l switch. After pulling the battery cable when I turn the switch from a4WD to 4h I can hear the relays switching then the vehicle goes into 4wd and the dash indicator shows four wheel drive. After a day or two nothing at all happens.

The 4wd logic and functions are controlled by the gem module. There is a very long pinpoint test procedure in the service manual to diagnose failure to shift between 4 hi and a4wd so it is not practical to post it.

If your certain disconnecting and reconnecting the battery re-activates the 4wd functions then the gem module may be at fault!?! No easy test to confirm though...

 

[Exia]

What year is the expedition, and motor?

Also the following links will explain your DTC codes and give solutions

OBD-II Trouble Code: P0401 Insufficient EGR Flow

OBD-II Trouble Code: P0174 System Too Lean (Bank 2)

OBD-II DTC: P0171 System Too Lean (Bank 1)

 

[Tacsat117]

I have a 1999 EB with the 5.4.
I will re-verify that disconnecting the battery allows the four wheel drive to function today. Is a gem module something I can get at a junk yard? Are they expensive when gotten from ford?

Thanks for the info!

 

[Exia]

They are a bit expensive, but I wouldnt trust one from a junkyard, some of them have a no-return policy on electronics.

ebay sells them new for 275.. there are some used ones but thats a 50/50 shot here is the link

YU7Z14B205AA Module Multi Function (Gem) 99 Expedition on eBay!

And to be honest I would focus on those DTCs, they " could be causing "some" of your problems

 

[Tacsat117]

Well I took Bessie to Ford today and they are saying the problem is the shift motor (congrats to whom ever called it early in the thread!). The tech said there was a code related to the shift motor (can't remember what it was and it's not in the paper work). He banged on the shift motor and it functioned. They recommended replacing it for around $600. When I got to the vehicle it did shift in to 4X4 but would not shift back out. I got it home and gently tapped the shift motor and it went into 2WD. Got greedy and tried it again. It shifted into 4X4 but won't shift back out. Tapping doesn't seem to work right now I'll give it some time and try again.

Thanks for the info all!

 

[Exia]

1999 FORD EXPEDITION Motor

You just saved 540 bucks