4 Wheel drive won't engage

[Turdchucker22]

Ok so I have a 2009 f350 SRW 6.4 with the electronic shift on the fly in the cab.

If I flip to 4x4 high I can hear the transfer case shift, but the hubs must not lock because I tried a 4x4 launch and would just roast the rear tires.4HI light comes on, on the dash.

But, if I get out and lock the hubs manually, all works fine and dandy and she's a rocket out of the hole.

Back in the cab with hubs set to automatic, put in neutral, and flip to 4lo, truck goes into 4 lo. No problem.

Here are my questions:
1.) putting the truck into 4lo you can feel how jerky it is, but there is no way to tell if the front wheels are engaging because the rears is also in low range also, correct?

2.) How to diagnose the the issue to get my ESOTF back to functioning properly.

Im a lazy son of a gun, and I don't want to be the guy who has to get out and manually lock his hubs on the job site when it gets sloppy.

 

[sleeperduty01]

Sounds like you have a vacuum leak for your from hubs or the little pump isn't working. I've seen some become unplugged from previous work. Id start there

 

[6.0 Tech]

Most common leak points are around the degas bottle. Brittle atic vacuum lines and removal of the radiator or degas and they like to.break.

 

[TexAg56]

Vacuum leak for sure. Cheap fix so be happy!

 

[morefuel]

Could possibly be the solenoid that controls the vacuum also.

 

[sootie]

Check if the vacuum pump is running. If it is, and not constantly, your hubs may need lubrication. If it isn't, check the fuse for it. It may have burnt out due to 100% duty cycle cause by a leak.