So Im trying to figure out how the 4x4 system, specifically the IWE's function in my 2015 4x4. With my 05 when the engine was running and the truck was in 2wd the front hubs were unlocked and the axles could free spin and then they would lock up when I selected 4wd. My 2015 however does not unlock the hubs with the engine running, at least in park. I can start the truck in 2wd, crawl under it and not be able to turn the axle shafts like I could in my 05. My question is, what is the normal operation of the IWE system and how do I check their function like I used to be able to do periodically with my old truck? The Auto 4x4 and regular 4x4 modes seems to be working with no warning lights on the dash so I assume everything is Ok but Id really like to make sure.

 

As far as i'm aware being in gear doesn't matter. But basically,

In 2WD with the engine on:
-the 4wd solenoid is open
-vacuum is supplied to the 4wd solenoid either by the engine through the check valve or the "vacuum storage box" on the firewall
-this pulls the ring gear in the IWE onto the hub and off of the axle
-you should be able to rotate the wheel without the axle moving
-the transfer case remains disengaged

In 4wd with the engine on:
-vacuum is still supplied to the 4wd solenoid, but the solenoid turns off the vacuum supply to the IWEs
-the IWE expands and it's ring gear slides onto the axle shaft meshing it with the gear on the hub
-the transfer case engages 4wd
-you will not be able to rotate the wheel without also moving the axle shaft

Easy things to check:
-with the truck running pop the vacuum hose leading to the IWEs off of the 4wd solenoid (I believe it's the bottom one), flip the truck between 2wd and 4wd, you should hear the vacuum and also hear it get cut off. My solenoid was acting funny until I unhooked the battery for 10 minutes
-with the truck off in 2wd, jack up the front and try rotating the front wheel it should rotate the axle shaft, this is because without a vacuum supply the IWEs will mesh the gears, you can unhook the vacuum hose connecting the IWEs to the solenoid to confirm that the IWEs are not getting any vacuum
-with the truck running in park and the front in the air switch on 4wd, you should not be able to rotate the front wheels as the t-case will have them locked with the immobile rear wheels

I'm sure I'm missing something or have corrections, so feel free to call me on it. I went through a bunch of 4wd issues on my cheap 2015.

 

So it should function the same as my 05, that means I do have an issue somewhere as my IWE's are not disengaging with vacuum. Thank you, I just wanted to verify that they didnt change the operation of the system from 05 to 2015.

 

correct this is my first f150, but it seems like nothing has changed in a while. I'd try a mityvac or something directly on the IWE to try and disengage it, if you can't build up vaccum chances are the IWE itself is bad. The good news is if your only problem is bad IWEs it's pretty easy and cheap (~$100) if you DiY.

 

Just as an FYI, the new trucks--talking '18 and up as that's what I've got--have a programmed function that will lock the IWE in for the first few miles of driving, ostensibly to lubricate the front diff. SO....if you do a cold start and check your front half-shafts immediately, they should be locked in until you have driven a couple of miles. Try driving around a bit then head back home and check for the front free-wheeling. I don't know when Ford went to this configuration, but hopefully someone will chime in with the first year of this feature.

 

I have a vacuum tester, Ill try that out. Thankfully the truck has a warranty so Ill go that route of I find an issue, it already is going in for a CV axle.

Good to know. I did check it this morning when I got to work before I shut the truck off but I will definitely check it again.

 

That warmup cycle started on the 2017. There's a couple variations AFAIK. '17, it comes into play at freezing +/-. The IWEs will stay locked in for 2 miles, then release. It happens on every key cycle as long as the temps stay at freezing or below.
The '18 IIRC, is similar, but it happens on start regardless of temp.
Here is the revised operation on the '19, 2019 F-150 - 4WD - Revised IWE Operation Strategy After Initial ***SSM 48088*** - Ford F150 Forum - Community of Ford Truck Fans