ESOF – DOA; OK out here someplace is the answer to my problem but I have not found with the search yet.

Earlier this summer the dash lights for the “4X4” and “Low” started flashing on and off with the ESOF dash switch in the OFF position. No matter what I did with the ESOF switch the indicator lights keep turning on and off until they stopped in about 10 minutes or so. This happened as I was driving to work on a paved dry road at 60 MPH in June. The 4WD never kicked. I have driven ESOF long enough to “feel” the 4WD coming in and out at that speed and it never did go in.
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Now nothing works! No indicator lights, no locking in or out in high or low or anything.
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I have put the ohm meter to the contacts of the ESOF switch and it appears to be OK.
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I have checked the plug on the transfer case and it appears to be making contact.
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I replaced the transfer case motor last winter.
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Last week on a business trip to Michigan</ST1 all of a saddened the 4X4 light came on, stayed on for about three minutes and went out. At the time I was driving about 70 MPH or so on the interstate and did not notice any change that I normally feel as the 4X4 engages/disengages at that speed.
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Also checked fuses and all appear to be good.
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Vacuum locking was working all of the past winter so I do not think that is the problem.
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So what’s up? Relays or something else?
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2001 F350, SD, 4X4, 7.3L PowerStroke, CrewCab, Longbed, six speed manual trans.
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Winter is coming and I just might needed the 4X4 soon!
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Thanks,
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Ron

 

Check the 4x4 module, I think it is the GEM module (expensive) take the cover off and see if it has any telltale signs of rust/corrosion and the have it checked at the dealer or shop that can do it. Also try switching the relays but it sounds like the module. Do some more searching also.