Gas Cap Light on 2004 Audi A4 Quattro

Gas cap light wwont turn off, replaced the gas cap already. How do i fix this?

I don't know about a "gascap light" so I assume you mean "check engine light."
The check engine light indicates that the computer has detected a malfunction in the engine/emission control system and has diagnostic codes and data stored which would be essential in diagnosing the problem.
A technician with a scanner can access the diagnostic codes and data and then be able to give you a diagnosis.
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