I have 2003 Altima, "service soon light is on, Dealer wants 78.00 dollars to Dign. And what ever cost to fix, Do you know where is coming from??

Is it actually service engine "soon"? If so, it indicates that you are getting close to a mileage milestone where some service is recommended. You can check the car manual for service intervals. Not sure if it will go away after the mileage is reached or only if the service is performed.

A Check Engine Light indicates a trouble code has been detected. For that a diagnostic reader has to be attached to read the trouble codes and determine the problem.