How can I reset the service soon light or would I have to take it to Mechanic?? on 2002 Saturn L200

I took it to my friend and he connected his computer to it and the coffee got was a 405 if I remember correctly it was a bad Gascony so since then I have replaced the gas cap with a new one

1 answer
You can try disconnecting the battery and waiting about 10 to 15 minutes and reconnect the battery. This should clear the light and reset the computer.