What Causes the Engine Warning Light to Come On in an Audi A4?

I recently purchased a used Audi A4 and the engine warning light keeps coming on. What could be the cause of this and should I be concerned?

The most common cause of the engine warning light in an Audi A4 is a malfunctioning oxygen sensor. This can cause a decrease in fuel efficiency and potentially lead to more serious issues if left unresolved. It is recommended to have this checked and replaced by a trained mechanic.

Another potential cause of the engine warning light is a faulty mass air flow sensor. This can cause issues with the air and fuel mixture, resulting in poor performance and potential damage to the engine. It is advisable to get this checked and replaced if necessary.