Once the fault has been corrected which caused your service engine soon light to come on in the first place you can do one of two things. Reset the light using a code reader or scan tool. Technicians will normally do this after completing a repair, your local auto parts store may also perform this service. The second way is to wait for the on board powertrain control module complete its system checks and turn the light off itself. This could take days or weeks depending on what the driving conditions were when the fault code as first set.