If the sensors in your vehicle are malfunctioning, the computer sets and stores a code. It then turns the service engine light on to alert the driver that there is a problem. Once you see the light, you can pull the codes yourself with an inexpensive code scanner available at auto parts stores. Once you pull the codes and match them against the code sheet, you can see which sensors are giving you problems. However, if your vehicle is throwing codes that don’t exist or do not make sense, you may have a bad computer. Since the computer cannot diagnose itself, it sends erroneous codes. If you pull the cover, you may also notice a burnt or fishy smell.