My GXP check engine light has just come on and a warning on my dash said something like "AC off to protect engine", then I noticed my coolant guage was not registering, is was below zero. Any suggestions? I went to autozone (I know, that as my 1st problem) and they ran a diag and said that it might be the coolant sensor. So I bought one, got home and cant find tht darn thing under the hood....where the heck is this thing at? ...and is this even the problem. Please help.