I have a 2006 Lariat F-350 4x4 DRW truck and I love it. I bought it with 125K on it and new I would have to put money into it which I have. Slowly getting the bugs worked out of it.

The lateset issue, now that winter is coming and I push snow around for my business, is that the shift on the fly will engage the transaxle as the 4x4 light goes on but will not lock the front hubs.

I did some investigating and found a vacuum switch mounted on the passenger side wheel well in the engine dept. One vacuum line goes to the vacuum canister and the other to the front hubs.

If I by pass the switch and apply vacuum to the front hub line the axle engages the hubs as to be expected and I have normal 4x4 operation.

If I try going through the switch no go. What tells the switch to activate turning on the vacuum to the front hubs?

I can manually turn the hubs to lock and I've got 4x4 operation and it works normally when I turn the 4x4 shift on the fly switch to high,low or off but I don't want to have to manually lock the hubs in and out.

Just can't for some reason get the vacuum switch to turn on locking the hubs when I have the hubs in auto.

Any help would be appreciated...

Thanks...

 

Turn your HVAC onto VENT or FLOOR with the fan speed on its highest setting. With the engine running, if you attempt to switch into 4x4 does the blower mode setting automatically switch to the DEFROST setting? By what you describe, I'm going to guess that it does. Because if so, your PVH solenoid (the part you described in your post) needs to be replaced.

 

I fixit PVH solenoid yesterday,just put WD-40 on it and blow carefully with air presure
works for me

 

I tried the HVAC on high to the floor. No change in modes. Stayed there.

Where did you spray wd-40?

Thanks for the replies. The solenoid may still be bad.

When I first tried it out a couple of months back I was able to get it to work normally. But after fiddling with it for a bit. Then it stopped working, like something is sticking.

 

Thanks m-chan68 and nasu77 for your help. I replaced the PVH solenoid and it seems to have fixed the problem. Wasn't sure until I got some feed back.

Thanks again guys...