Hi all... I own a stock 01 GMC Sierra 2500HD 8.1 with 55K. Shift indicator started going out, truck wouldn't go into 4LO & was acting up shifting into reverse. Did some research & figured it's the NSBU. I've got the black one on mine and have the new brown one in my hands. My truck yesterday went into what I'm assuming is "limp" mode. Won't shift out of 3rd, check engine light is on. My question is did the faulty NSBU switch cause it to "limp" or is there another problem? It's doing the same thing today after sitting all night. Also, when I change this NSBU today will it reset the code or can I just unhook the battery to reset it? Any help would be appreciated.

Your code will still be there but it will go bye bye after a few ing cycles and it will work if the NSBU switch is the problem.

Check the DIY forum there is a good write up there. Read the whole thing.

Othere things can cause it but I'm willing to bet your NSBU switch took a crap

Also you know that its covered untill 100K? Look at the top of this forum. Its an easy change yourself though.

Thanks for the input, just wanted to make sure I didn't screw the tranny up. I read all the info before posting and was pretty sure the NSBU was the culprit, just was wondering about it making the truck "limp". I checked the article on the warranty and it looks like that is for diesels, mine is a 8100 gasser. Sorry for posting on a "diesel" forum, but you guys sound like you know your allisons.:D