Why does my Audi A4 have reduced engine power?

My Audi A4 has suddenly experienced a significant decrease in engine power and has a yellow warning light on the dashboard. What could be causing this and how can I fix it?

The most likely cause for your reduced engine power and warning light is a faulty oxygen sensor. It is important to have this diagnosed and replaced by a certified mechanic.

Check your air filter and replace it if it's dirty or clogged. This can significantly impact your engine's performance and is a relatively easy and inexpensive fix.