The Audi S3 fog light requires a bulb size of H8 for the lighting components. Data for the specific bulb requirements covers the range from 2015 to 2016.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The H21W is the most frequently specified bulb across the Audi S3 fog light data, appearing in the rear fog light position for the 2015-2016 and 2019-2024 model years.
The H21W operates at 12V and 21W, uses a BAY9s bayonet base, and is rated under the ECE standard, meaning it meets European and international regulatory requirements for signalling applications.
The BAY9s base on the H21W is an offset bayonet fitting, which is not interchangeable with standard single-contact bayonet bases such as BA15s, making socket compatibility a relevant consideration during replacement.
The H8 bulb is specified for the front fog light on the Audi S3 for the 2015-2016 model years, operating at 12V and 35W with a PGJ19-1 base.
The PGJ19-1 base used by the H8 is part of a family of projector-style bases that includes PGJ19-2 and PGJ19-3, each sized differently; substituting one for another is not supported by the specifications.
The H8 carries ECE approval and is also approved for use in the United States, reflecting its acceptance across both regulatory frameworks.
The 2019 rear fog light entry specifies the H21W with the additional qualifiers "Halogen" and "Inner," indicating a positional or assembly distinction within that model year's rear fog light configuration.