Under the dash near the peddals. If you can take your vehicle to an auto parts store, they will run the diagnostic test for you, free of charge. Just walk in and tell them that you need a diagnostic scan run on your vehicle and tell them which make and model. Its like a mini handheld computer with different fittings they will hook to your outlet under your dash and it will tell them whats wrong with your vehicle, they can also erase any codes temporarily that keeps the dash lights on for a while until you get the problem fixed.