The check engine light in your Audi alerts you to potential system issues affecting performance and safety, often indicating specific malfunctions through emitted codes. Common reasons for the light's illumination include spark plug failure, catalytic converter issues, oxygen sensor malfunctions, mass airflow sensor problems, and simple fuel system errors like a loose gas cap. It's essential to promptly diagnose and address these issues, ideally with a specialist, to maintain the vehicle's reliability and safety.