I have a 2006 f350 6.0L diesel and I’m having a solenoid issue.

I have tested my hubs and all my vacuum lines and the entire system after the solenoid holds vacuum and works great.

When I engage the 4x4 the solenoid works and pulls correct vacuum, however after 45 seconds or so it’s dumps the vacuum and the 4x4 will no longer work. I originally thought it was the solenoid so I replaced that but the next one does it too.

I have also checked vacuum pump and reservoir and they both work as should so I’m left thinking this problem is solenoid/electrical related.

Any one know where I go from here!?

Thanks!