The Audi TTS Quattro fog light requires a bulb size of H21W for the front lighting assembly. Available information covers the specific range from 2009 through 2014.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The H11 bulb is the most frequently specified type across the Audi TTS Quattro fog light data, appearing as the front fog light bulb for every model year from 2009 to 2015.
The H11 operates at 12V and 55W, making it a higher-wattage halogen unit relative to signalling bulbs. It uses a single filament and a PGJ19-2 base, which is a keyed connector that prevents substitution with physically incompatible halogen types.
The H11 carries ECE certification, meaning it meets European and international lighting regulations, and it also holds approval for use in the United States.
The H21W appears in two distinct roles across the Audi TTS Quattro specifications: as a front turn signal bulb for the 2009-2010 model years and as the rear fog light bulb for the 2011-2014 model years.
The H21W operates at 12V and 21W, classifying it as a signalling bulb rather than an illumination bulb. It uses a BAY9s bayonet base, which is offset to prevent incorrect installation of a bulb with the wrong wattage or filament type.
The BAY9s base on the H21W is not interchangeable with the PGJ19-2 base on the H11. The two bulbs serve different sockets and cannot substitute for one another despite both operating on 12V systems.
For the 2009 and 2010 Audi TTS Quattro, the front fog light assembly requires two distinct bulb types simultaneously: the H11 for the fog function and the H21W for the turn signal function within the same general assembly area.
Both the H11 and H21W are single-filament bulbs, meaning each performs only one lighting function. Multi-filament alternatives are not listed for any position in these specifications.
The rear fog light position on the Audi TTS Quattro is specified only for the 2011-2014 model years, with the H21W designated for that application across all four of those years.
The 55W rating of the H11 places it in a wattage class that generates significant heat during operation, a factor relevant to housing compatibility. Substituting a higher-wattage bulb in an H11 socket risks damage to the lens or wiring harness.