Denso vs NGK – Which Spark Plug Is the Better Choice? Maintenance Tips 1 2 3 4 TABLE OF CONTENT 1. Top 5 Reasons of Audi Check Engine Light in ON 1. Spark Plug Or Plug Wires 2. Catalytic Converter 3. Gas Cap 4. Mass Airflow Sensor 5.Oxygen Sensor 2. FAQs ...