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Discussion Starter #1 (Edited)
My front hubs do not lock when set to auto.They work fine when I set the hubs to lock.

The truck has ESOF and the ESOF works and shifts the transfer case with no problem.

This problem has existed since new. I now have 6800 miles.

Dealer is about 100 miles away so before I make a a 200 round trip and lose use of the truck for a day or more I want to look into the cause.

Any input as to the potential cause is welcome.

Thanks

2008 F350 4X4 DRW King Ranch Job 3
 

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i have the same issue. I was told by the dealer that there is a vac solenoid on the right side of the engine compartment around the air filter housing somewhere and he said that is almost always the problem. Have not had time to check mine out, taking it in for differential problems so while it is back stock I will have them fix that as well. Will let you know what they find.
 

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my old one did that and when it did it was a blown 10 amp fuse
 

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One of my trucks had an issue with it not engaging and got me stuck. I found later that the wire for the vacuum pump was off. From what I found, you can hear the pump turn on when you put the ignition to the on position ,after sitting for a while. To help isolate issue, first thing in the morning after a cold soak, put the ignition in the on position.(You should hear the pump turn on), wait for it to build vacuum pressure and turns off, this will prove nthe pump works. Then turn the 4wd high switch on, the pump should run again along with hearing the shift motor engage. wait for the pump to stop again. The pump cycle takes a while to build, just to be safe, give it 5 minutes to stop. If it doesn't stop pumping you have a leak somewhere. If it stops for the ignition being turned on and not the solenoid, there is a leak somewhere after the solenoid. If it doesn't stop after the ignition only, it is between the two. If you can't figure it out from this you will most likely need the dealer trip.
 

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If you have vacuum in the system, next thing to check is the soleonoid for the hubs. The solenoid for the hubs is located on the passenger side of the fan shroud.
 

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Just got my truck back from the shop, it was the solenoid. Something that i noticed is that before I took it in my vacuum pump ran all the time, now it does not so it must have been a pretty serious leak...
 

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Beach Bum
2014 F250 CCSB 4wd
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One of my trucks had an issue with it not engaging and got me stuck. I found later that the wire for the vacuum pump was off. From what I found, you can hear the pump turn on when you put the ignition to the on position ,after sitting for a while. To help isolate issue, first thing in the morning after a cold soak, put the ignition in the on position.(You should hear the pump turn on), wait for it to build vacuum pressure and turns off, this will prove nthe pump works. Then turn the 4wd high switch on, the pump should run again along with hearing the shift motor engage. wait for the pump to stop again. The pump cycle takes a while to build, just to be safe, give it 5 minutes to stop. If it doesn't stop pumping you have a leak somewhere. If it stops for the ignition being turned on and not the solenoid, there is a leak somewhere after the solenoid. If it doesn't stop after the ignition only, it is between the two. If you can't figure it out from this you will most likely need the dealer trip.
i did that test on mine. put the key on on and the pump ran for a min or two. then turned off and didnt come back on. then put 4x4 on. pump came back on and ran for like three or four mins. went off and it didnt come back on. and i also pulled the hose off the hub on the pass side and felt no vac. so that would mean i have a leak somewhere betwen the solenoid and hubs?
 

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If you pull the vacuum line from the axle with the 4x4 engaged and the pump doesn't operate with the self made leak, there is a clog or kink somewhere, or more likely the solenoid.
 

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Beach Bum
2014 F250 CCSB 4wd
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If you pull the vacuum line from the axle with the 4x4 engaged and the pump doesn't operate with the self made leak, there is a clog or kink somewhere, or more likely the solenoid.
i did that too lol. just to see if i could hear the vac excaping. non what so ever. i guess its time to track down the lines :doh:
 

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Let's revive this thread

I have the same problem 4wd not engaging when on auto setting. And when I pull the plug that goes into the PVH solenoid and test it for power the center pin isn't getting any voltage so I checked fuse #34 which was fine. Anyone know what I should do next? I thought it was the solenoid but if it's not getting power I'm assuming the problem is before that?
 

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If you have vacuum in the system, next thing to check is the soleonoid for the hubs. The solenoid for the hubs is located on the passenger side of the fan shroud.
The Soleonoid was my problem....the location is on top of the fan shroud on passenger side.
Can't miss it and takes about 2 minutes to change out.
 

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Yeah. My solenoid was bad too and I had to run a new power wire from the vacuum pump to the solenoid because it wasn't getting power for some reason.
 

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4HI or 4LO, if 4LO then I would say normal. I have an 08 FX4 personal truck and we have an 09 450 4X4 XL at work, whatever reason the hubs while set in AUTO won't engage in 4LO, you have to lock them in manually for 4LO. But they both engage fine into 4HI in AUTO. I would assume it would have to do with the added torque of 4LO, that they want it manually locked for sure measures due to the torque advantage in 4LO. But if anyone knows more please respond.
 

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My pump has been running for a while now and just realized its use when it snowed today and 4WD wasn't working. So I obviously have a vacuum leak somewhere because my pump WILL stop immediately when I put my finger over the line. Does anyone know where I can get replacement lines from OR what size the hose is so I can go get some new hose and rune new lines? I have the pump unplugged for now.
 

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I've been working on mine, and determined that everything worked and that there is a leak on the driver's side. That side will not hold a vacuum. I pulled he hub the other side and put it on the driver side, no deal. So the problem must be axle seal or something. So then sprayed soapy water on the back of the rotor assy, and applied a small amount of pressure. Bubbles, so I have it isolated. It comes apart this morning.
 
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