I drove it to the auto parts store the day it threw the code and it drove fine. The store was only like 2 miles away but the truck drove fine without any hard shifting or anything.

How is the neutral switch replaced? Where exactly is it located and where does it go?

How do I test it? It was throwing code P0847 and P0700. P0847 is related to the shift valve d solenoid. I was just going to replace that solenoid, since you work on these transmissions is that what the problem is?

From what I've seen, those Allisons are like black magic, not many who really know the deal other than Diesel Tuners, GM/ Allison really locked them down, you may need to take it to a reputable dealer or GM diesel specialist, but, behind the 8.1, should be minimal issues, it takes a lot of torque to damage them but the electronics can drive you crazy at times, find a diesel/ allison specialist and have them take a look if you don't have a good dealer near you... Sorry i'm not more help, haven't owned one myself... Yet...

That trans is not 100 % allison,,it uses's a gm valve body with gm shift solenoids and all the sensors.

I had the dealer fix mine. Actually they replaced it twice. I had the truck in for an oil change and they replaced it at 31k because they noticed the insulation on the wires was coming off. Then at 37k(1k out of warranty), the trans started acting goofy. They ended up replacing it again as a defective part. Never had a problem after that with another 100k on the truck. Its an electronic module that is mounted on the exterior of the trans.

The park/neutral switch is mounted on the drivers side of the trans. The new updated switch comes with a heat shield to protect it from the exhaust. The old switches would melt the resin inside and seep through to the wire pigtail and glue them together often causing the plug and harness end to be replaced together. The dealer sells a replacement pigtail but they do not give it away, its more than the switch if I remember correctly. By the way this was the only issue I have ever had with my 8.1/allison.

The switch is known to be a problem but before replacing anything verify what your problem is before replacing anything as it may have nothing to do with your current code.

Well guys just wanted to give everyone an update, I went to go to the auto part store to buy the neutral safety switch the other day but when I started it up the check engine light was not on anymore. Drove it around, towed the boat and the check engine light never turned back on. Wierd but I'm not complainaing, no more check engine light so that's good.

Boatnt, brian41 and everyone else, I wanted to thank you guys for helping me and guiding me in the right direction. You guys rock!!!