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I have a 1999 F350 super duty 4x4 dually. Twice I have put the transfer case in the low range position to pull a trailer up an incline. When I finished the pulling I put the transfer case back into the high position but it failed to go into high range. I had to take it to the Ford dealership to get it back in high range..The dealer said it needed a new switching motor and a new gem module. I replaced the switching motor. About 4 months later I again put it in low range only to have the same problem with it not coming out of low range. Is the problem the gem module? Does it control the switching of the transmission or transfer case?
 

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^^^^^^^ there’s a different sequence for 4 LO (engaging / disengaging)

I actually thought it was Park, foot on brake - but neutral might work
 

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I went back and looked at a lot of posts....and as Nick said “Neutral”

and I’m seeing sequence to leave 4 Lo as: stop, put in neutral, foot on brake, shift selector from 4 Lo to 4 Hi, wait for the clunk, put in drive, and while moving select 4 Hi to 2 Hi.
 
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Unsure of GEM but as for the switching motor:

How did the Dealer get it out of 4-LO?

Only two methods I am aware of are by engagement of the switching motor or by hand underneath the truck with the switching motor removed.

It would seem to me that the GEM issue would be an electrical (signal) issue while the switching motor would be a mechanical issue.
It also seems unlikely they would both fail at the same time.

There is a troubleshooting instruction somewhere in the archives for the ESOF Transfer Case. I think by a fellow named Rusty, and it helped me diagnose.

I will try and search for it.
 

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