Audi S4 Fog Light Bulb Size

Additional Notes

• The H11 bulb is the most frequently specified front fog light bulb across the Audi S4 model years covered, appearing in six consecutive years from 2007-2012. It operates at 12V and 55W, uses a single filament, and is fitted with a PGJ19-2 base. It follows the ECE standard but also carries US approval.
• The H8 bulb shares the same 12V operating voltage as the H11 but draws only 35W, making it a lower-wattage single-filament halogen. It uses a PGJ19-1 base, which differs from the PGJ19-2 base of the H11, meaning the two types are not interchangeable despite their similar appearance and shared ECE and US approval status.
• The 2018 Audi S4 front fog light uses the 921 bulb, a wedge-type T15 unit rated at 12V and 16W under the ANSI standard. This is the only ANSI-standard bulb in the front fog light specifications, and it is not interchangeable with the ECE-standard halogen types used in other model years.
• The H21W bulb is specified for the rear fog light position across the 2019-2024 model years, with 2022 not listed in the data. It is a single-filament signalling bulb rated at 12V and 21W, fitted with a BAY9s base, and governed by the ECE standard.
• The 2019 rear fog light fitment carries an additional qualifier, noting that the H21W applies specifically to halogen inner configurations without special body measures, using standard-design taillight assemblies. This indicates that alternative configurations on the same model year may not share the same bulb requirement.
• The H3 and H7 bulbs, specified for the 1992-1994 and 2000 front fog light positions respectively, both operate at 12V and 55W but use distinct bases. The H3 uses a PK22s base while the H7 uses a PX26d base, and neither is physically compatible with the PGJ19-series bases found in the H8 and H11 types used in later years.
• Across all front fog light entries, the wattage ranges from 16W for the 921 wedge bulb up to 55W for the H3, H7, and H11 halogen types. The H8, at 35W, sits between these two extremes. These differences in wattage reflect distinct electrical load requirements that are specific to each model year's wiring and socket design.
• The base type is a primary factor governing bulb interchangeability throughout these specifications. The PGJ19-1 (H8), PGJ19-2 (H11), PX26d (H7), PK22s (H3), BAY9s (H21W), and wedge (921) bases are each mechanically distinct, and substituting one bulb type for another across these base families is not supported by the specifications.