The ecu is the on board computer for your car. It controls many things like air fuel ratios, timing, ignition and more. Depending on what you drive, it could be a small computer or a "MAC" daddy of a computer. If your car is showing dash lights or check engine lights, the ECU will tell us what is wrong with your car. In most cases you just need to have the ECU rebooted like your home computer. We can do this for you too!