The Audi Q3 tail light requires a bulb with the unique size of P21W for proper installation and function. Data for the specified lighting component covers the range from 2017 to 2018.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 921 bulb follows the ANSI standard used in the United States and Canada. It is a T15 wedge-base bulb rated at 12 volts and 16 watts, and it fits the inner tail light position on the Audi Q3 for the 2023-2024 model years.
The 12961 is a Philips part number designation for a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12 volts and 5 watts. At 5 watts, it draws significantly less power than the 921, reflecting its use in a lower-intensity inner tail light application on the 2020-2021 Q3.
The inner tail light position on the Audi Q3 uses different bulb sizes depending on the model year. The 2020-2021 years use the 12961, while the 2023-2024 years use the 921. These two bulbs are not interchangeable, as they differ in base type, wattage, and physical size.
The P21W follows the ECE standard, which is used in Europe and internationally. It is a single-filament signalling bulb with a BA15s bayonet base, rated at 12 volts and 21 watts. The bayonet base requires a twist-and-lock installation, which is mechanically distinct from wedge-type bases.
The outer tail light position on the Audi Q3 uses the P21W across all listed model years, spanning 2017-2018 and 2020-2024. This consistency means the outer tail light socket and bulb type remained unchanged across those years.
The P21W and the 921 are not interchangeable despite both being rated at 12 volts. The P21W uses a BA15s bayonet base, while the 921 uses a T15 wedge base, making them physically incompatible with each other's sockets.
The single-filament design of the P21W means it serves one lighting function per bulb. This contrasts with dual-filament bulbs, which can handle two functions such as braking and running light within a single unit.