Genuine OEM Audi Ignition Switch, part number 4B0905851Q. This essential component is responsible for controlling the vehicle's electrical power supply and initiating the engine start sequence. It is typically mounted on the steering column, often incorporating the steering lock mechanism for security. Constructed from durable cast metal, it weighs approximately 0.378 kg and measures 0.133 meters in length. Choosing a genuine OEM ignition switch ensures precise mechanical and electrical operation, correct key cylinder interaction, and seamless integration with the vehicle's immobilizer system, which is crucial for both security and reliable starting.