What are the common reasons for a check engine light to come on in an Audi A4?

I'm currently experiencing a check engine light in my Audi A4 and I'm wondering what the potential causes might be. I've checked the gas cap and it seems to be tight. What else should I be considering?

One of the most common reasons for a check engine light to come on in an Audi A4 is a faulty oxygen sensor. This can affect the car's fuel economy and performance. My advice would be to take your car to a trusted mechanic for a diagnostic check to confirm if this is the issue.