4 wheel drive not disengaging

[bdreker]

I have a 2011 Expedition EL with 175k miles on it, owned it since new. We used the 4WD a lot last winter with higher than normal snow in MT. In the spring I noticed some resistance and tight steering when driving on dry roads and it feels like the 4WD is engaged, even though the switch is in 2WD. I found some late season snow to test, and the front wheels do not spin in snow in 2WD, but they do spin with switch in 4WD as its supposed to. But with switch in 2WD the front drive shaft is still engaged and spins between the transfer case and front drive shaft. I believe when in 2WD the driveshaft is supposed to be stationary. I took it to my mechanic and he says all is fine, but I've driven it for 95% of its 175k miles and I still think the front drive shaft is engaged when it is in 2WD, but the hubs are just not engaged. I put my cell phone on the ground in video mode and drove over it in 2WD, 4WD high and 4WD low and the drive shaft turns in all modes. I'm thinking a bad actuator.

 

[twodollars]

I'd check the vacuum solenoid. Vacuum is applied to disengage the front wheels from the half shafts, so the planned failure mode is have the front wheels locked. My guess is that's what is happening on yours. Transfer case sounds like it engages and disengages as intended.

 

[ExplorerTom]

I’d bet your IWEs have failed.

I tried diagnosing my vacuum system and I couldn’t replicate the noise I would get in 2wd that would go away in 4hi. The vacuum system appeared to be good, but it acted like my hubs were engaged. I bought some RCV hub lockouts and haven’t had a noise since. Yes, my front driveshaft does spin in 2wd, but doesn’t seem to effect MPGs much. I still average like 14-16.

 

[Dustin Gebhardt]

The front system is fairly easy to troubleshoot as it is purely a vacuum-based system (with the exception of the solenoid valve). You will need a vacuum pump (like a My-T-Vac) with a gauge. I don't have the schematic in front of me, but there are only a few things to check:

1. Find the vacuum hose that supplies the system. Make sure that it is intact. Plug one end and pull a vacuum on the other end. Does the vacuum hold? If not, then replace the hose.
2. There should be a check valve on this hose. Test the function of the valve by drawing a vacuum on each end, one end at a time. It should hold a vacuum in one direction and not hold any vacuum in the other direction.
3. Find the vacuum reservoir. Pull a vacuum on the reservoir and verify that the vacuum holds. If not, replace the reservoir.
4. There should be a tee between the reservoir and the check valve. That tee should go to the solenoid. Pull a vacuum on each side of the solenoid (there should be an inlet and outlet). Then energize the solenoid with a 12V source. It should hold a vacuum one way (energized, I think?) and not hold a vacuum the other way (not energized, I think?).
5. The outlet from the solenoid should go to the IWEs. While at the solenoid, pull a vacuum on the line going to the IWEs. It might take a while to pump down, but it should hold a vacuum. If it doesn't, the line or the IWEs are bad. In my case, this was the problem for me. The line that runs across the front crossmember was worn through. I cut out the worn section and spliced in a new line.
6. Disconnect the double-tube at the IWEs and pull a vacuum. They should hold a vacuum if they are working. If the vacuum leaks down, they are probably bad.

My '07 has 4 modes: 2H, 4A, 4H, 4L. In 2H, the front driveshaft doesn't turn. In all other modes, the front driveshaft turns. In 4A, the front axle half-shafts do not turn unless called for my the traction system. In 4H and 4L, the front axle half-shafts are always turning.

 

[jimbosidecar]

I realize we're talking apples and oranges but I have a 2001 Expedition with the bigger V8 engine. I have AWD 4H and 4L (I think). I almost always leave it in AWD. But recently when turning it feels like the front tires are scrubbing like it's in 4WD. Does this also sound lie a vacuum issue? And just recently by rear differential started acting up. It would make noise at the passenger rear wheel, and vibrate badly making the vehicle slow down. I made it home (about 70 miles) on the hiway at about 55-60 without trouble, but when I got to normal roads st started up again. I opened the differential at the rear and the oil looked brand new and all the gears look new and sharp. It's got all 4 wheels off the ground now and spinning the rear wheel by hand it doesn't sound or feel like a wheel bearing. Any ideas where I should be looking?

 

[ExplorerTom]

I realize we're talking apples and oranges but I have a 2001 Expedition with the bigger V8 engine. I have AWD 4H and 4L (I think). I almost always leave it in AWD. But recently when turning it feels like the front tires are scrubbing like it's in 4WD. Does this also sound lie a vacuum issue? And just recently by rear differential started acting up. It would make noise at the passenger rear wheel, and vibrate badly making the vehicle slow down. I made it home (about 70 miles) on the hiway at about 55-60 without trouble, but when I got to normal roads st started up again. I opened the differential at the rear and the oil looked brand new and all the gears look new and sharp. It's got all 4 wheels off the ground now and spinning the rear wheel by hand it doesn't sound or feel like a wheel bearing. Any ideas where I should be looking?

A4wd.

In your underhood fuse box, remove fuse 104. This is the transfercase shift motor fuse. See if the issue goes away (it did on my 2000). Because this fixed my issue, I did the Brown Wire Mod and turned my a4wd into 2hi. I still had 4hi, 4lo capability (once I out the fuse back in).