1999 service 4wd issue

Black99

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Got a weird one here. Here is what happens:

-be in 2wd
-push button to go into 4w high
-truck successfully goes into 4w high
-after about 15-20 seconds, service 4wd light comes on
-try to switch back into 2wd and truck will not do it, light on switch does not blink or anything, it doesn’t even try
-shut truck off and wait a few seconds
-turn key on without starting truck or just start the truck, and immediately press button for 2wd
-truck successfully switches back into 2wd
-no more service 4wd light

It does this every time I use the 4wd. I have replaced the button panel which did not fix it. Also recently replaced the encoder motor and that didn’t fix it ethier. Isn’t the only thing left that it could be is the TCCM? I’m lost for ideas on what this could be haha. If it was the tccm, wouldn’t it not even switch at all? Truck has 205k miles on it. Any ideas are appreciated!
 

drakon543

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there's shift sensors on your transfer case aswell and the front axle if i recall. if the 4wd shift position switches are getting faulty if the tccm sees an intermittent signal it can cause all kinds of wierd stuff. as exp stated the tccm has its own fault codes that are quite helpful here as its a pretty simple system it can typically point you directly to the issue.
 

Black99

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is the only way to get tccm codes with the tech2 scanner? just a regular obd scanner won't work in this case right
 

Fless

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Some higher level (non-Tech 2) scanners will read Chassis codes (Cxxx). Just need to find one that does.
 

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