Tried to turn on the 4wd during the snow this week. The light on the dash would not light up. I locked the hubs in manually, not sure if that supplied power to the front wheels or not. From researching the issue here on the forums it sounds like this could be a vacuum issue. I will look into this. If anyone has any experience with this I would be grateful to hear from you.
Did I have power to the front wheels by locking the hub in manually???
I'm having the same problem ! To answer your question though, even if you locked the hubs manually, you won't have power unless the transfer case is engaging, which it probably isn't if the light's not coming on. I'm assuming you have ESOF and not a manual shift TC. A vacuum problem will keep your hubs from enaging (hence the manual option) but the TC is shifted by an electric motor, not vacuum. What kind of truck do you have?
I have a 2000 Excursion 4x4 7.3 Diesel Limited. I think I have basically eliminated everything except for possibly something electronic. I put a vacuum on the hub at the rotted vacuum line and the hub assemblies at both sides were holding a vacuum. I am thinking that the electric motor and switch at the transfer case might be the issue. Or possibly the switch at the dash. I am going to pull my tester out tomorrow and check. I will let you know what I come up with. Hopefully one of us will be able to find the problem and help out the others.
whoops. I put the vacuum at the hub assembly where I replaced the rotted vacuum lines. The vacuum held for 15 minutes plus. So, I am thinking that all the seals at the hub are working. ( however, I think I may have a leak in the outer axle seal, finding a bit of oil gathering up there, nothing to do with the 4wd though...)
We solved the hub engagement problem by replacing the vacuum switch (not sure if you call it a switch, little plastic thingy that the lines go into) under the hood, it was full of crud. If it's something simple let me know! I suspect my problem has something to do with the ECM, if that's not working right it will manifest itself in all kinds of odd ways. Before the 4wd quit working it would shift in and out on it's own. I'm looking for a wiring diagram so we can start eliminating some things.