W4500 Won't Shut Off

autoworks · January 1, 2009

I have a 05 GMC 4500 with a 6 L gm engine, It won't shut off in park or neutral,it will shut off in any other gear{auto trans.} I have replaced the neutral safety switch and disconnected the ign. switch. I have very little info on these vehicles, any help would be very helpful,this is a university vehicle and they would really like to get it back.

pennzoil29 · January 1, 2009

That's strange. Have you scanned it for any codes? Does it start in P/N, or in any gear?

By the way, welcome aboard.

TexasAl · January 1, 2009

Perhaps your gear range switch needs to be adjusted.

dietz4ibanez · January 3, 2009

BTW Welcome to the site! :bump:

autoworks · January 3, 2009

That's strange. Have you scanned it for any codes? Does it start in P/N, or in any gear?
By the way, welcome aboard.

Thanks for the reply. I found the problem last night after about ten hours of testing, the diode trio is burnt in the alt. and is putting a/c voltage thru the ecm.Installed a new alt. and it works fine.

BuckFeverZ · January 3, 2009

Glad ya got 'er figured out.

DofD · January 7, 2009

Hi there and welcome to GM Trucks! Glad to hear you found and fixed the problem.

autoworks · January 7, 2009

unfortunately it only shut off for about 2 days and is back with the same issue, the owner has another truck he is going to bring over so I can do some testing on that to see were the difference is,right now I am thinking that the ac voltage has damaged something in the ecm.