My 2002 Impala is having issues. The service vehicle soon light come on then the battery light will flash and then the security light will come on and the message "locked" will apear on my radio when it does all of this at the same time it will not allow my AC to work. I have changed the alternator and battery but dont know what else to do. I dont want to spend alot of money by taking it to a dealership.. PLEASE HELP!!