While living in Indiana I had no problems with my 2001 Impala. I drove the car from Indiana to Phoenix and had no problems the entire way. It is the hottest time of the year in Phoenix and now that my car has been in the heat for several weeks it's been starting to do odd things. When driving in the heat the "high beam out" and "security" light will come on. The dash lights will also dim when in a dark area, but the headlights remain strong. I had the battery tested at autozone and it tested out fine. I know about the common Passlock problem with chevy's, but have had no problem starting my car even after the security light appears. I suspect it is directly related to the heat, but I am unsure what to do to fix the problem. Thanks for any suggestions.