I can't offer much advice but you might want to try putting the transfer case in Low and seeing if Manual Mode also shuts off by itself. That could be a clue that it's a switch problem, or something bigger.

 

I would guess it's something loose under the shifter. Mine didn't come on at all when I first bought my truck. I took the shifter cover off and cleaned everything out and re attached and it's worked fine since.
Good luck.

 

Quick update on this
switched to my all season tires as I don’t plan on doing off-roading anytime soon
they are stock size tires. Sport mode light now stays on as it should
I’m guessing because I had the all terrain tires a bit bigger 265/65/18 it kicks out the sport mode light almost instantly

 

Different tires will have no effect on the Sport Mode or Manual Mode function. I'm willing to bet the frame to the PRND321 assembly is either cracked around the momentary switch for Sport/Manual button. I've seen plenty look perfectly fine externally, but once removed the plastic is either busted, cracked or debris is in it.

 

Well it works now that I got my original tires back on. So it must

 

I’m telling you there is nothing that changing tires would do to effect the electronic Sport/Manual function on a D2. I’ve gone from oversized off road tires to street tires many many many times over the years & there is absolutely nothing the D2 is going to magically detect from different tires or rims.

Anything past 06 will more than likely have TPMS sensors for detecting air in the tires, but thats it. I’m still willing to bet something probably got stuck under it or the PRND321 assembly is lightly cracked underneath & it effected the momentary Sport/Manual mode button. I’ve had D2’s not engage Manual Mode at all due to a bad switch on the TC, but once again that had nothing to do with simply swapping tires out.

 

Ran sport mode in both my 01 and 03...with 265/75R16's. Agree with Best, the system has no idea what size tire your running. There's such a thing called...coincidence...when working on cars or making repairs.

Brian.

 

Well for the past year sport mode does not stay on for more than 5 seconds. Only one way to find out if it’s tires One day I’ll switch back and forth and see
I thought maybe tranny had a speed sensor and maybe didn’t match the speedometer type thing

 

Would mismatched wear on the tires resulting in a different rolling radius at one corner cause the TCU to freak out?