SERVICE ENGINE SOON light ON. No codes present.

Hi! I have a 1994 Cadillac Eldorado. I already posted a thread here about this SERVICE ENGINE SOON light and a SERCICE RIDE CONTROL message. Thanks to members of this forum I got rid of the SERVICE RIDE CONTROL message. But my problem now is the SERVICE ENGINE SOON light.

I already did check on the battery as one of the members here told me. I removed the negative cable for like 10-15mins. When I ran the car, after less than a mile running the light came on again. There are no codes that are current now on the diagnostic panel. I even had it removed with the help from a mechanic but still it comes back. Can't feel anything wrong with the car whatsoever, but I know I shouldn't rely on that feeling either.

Though I can smell strong scent of gas as soon as I enter and leave the car from a trip. I already checked the gas cap too.

I'm about to renew the registration of the car and a smog test is needed by the DMV here in CA. I'm already aware that a Service Engine Soon light automatically fails the test. Please help me. Any idea that can help me with this is greatly appreciated. Cheap repairs to serious repair ideas would most likely be needed.

THANK YOU IN ADVANCE!