08 4x4 trouble

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Nov 20, 2011 | 07:12 AM

cabbie

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08 4x4 trouble

I have a 08 f250 electronic shift truck, the 4x4 doesn't work the light comes on can hear it shifting but no 4x4, also the back light on the switch isn't working. I haven't checked the fuses yet bacaue I've been working. Any suggestions?

Last winter I had the hubs and module replaced under warranty and they also said a plug? was disconnected. Anyone know where this plug? is located so I can check this. Truck is out of bumper to bumper warranty, but still has powertrain coverage, think this will be covered?

Know this is long winded, just looking for suggestions

Thanks

Nov 20, 2011 | 07:33 AM

PA-Mark

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From: Mt. Holly Springs, PA

neither does mine.... here is what i have found out.

First thing to check is the fuses.... but after that, put the hubs in manual lock and see if that works. If it does its most likely a vaccume problem.
Above the fuse box in the engine compartment is an aux vaccume pump.
This vac pump is set to run all the time (key on) to maintain a min vac then shut off. I cant remember what the min is but when i was testing mine i looked it up. I hooked mine up to a vac guage turned it on, it pumped up to pressure then shut off. I bled off a bit of vac it kicked on then off when at the proper level.
From there if that is correct, its time to test individual vac lines. I went down to the hubs just to rule them out. Disconeccted the lines one at a time, put my vac tool on it and with a minimal amount of press it locked the the hub and maintained the pressure. Then i did the other with the same result. If that is all good its time to go point to point with all the vac lines. I narrowed mine down to a switch that lets the vac pressure down to the hubs, mounted on the radiator.

I hope this helps, Mark

P.S. I still have not fixed mine. I dont use it enough, If i need it I just put it in manual

Nov 20, 2011 | 08:24 AM

PA-Mark

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From: Mt. Holly Springs, PA

Oh ya, if you get to the point of point to point testing of the vac lines, its alot easer to remove the plastic inner fender wells.

Nov 20, 2011 | 08:38 AM

senix

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From: Frederick, MD

If you switch to 4x4 and your heating or ac defaults to defrost then you have a vacumn leak. Look at the hubs and work your way backwards.

Do manually lock the hubs in and verify operation as well.

Nov 20, 2011 | 11:06 AM

cabbie

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works when hubs are locked

4X4 works when hubs are locked, so is this a vac issue? Haven't checked the fuses yet but makes sense that it is a vac issue if the hubs are locked ( not enough pressure to lock the hubs? ) does this make sense?

you think this is covered under powertrain warranty?

Thanx