Audi TT Back Up Light Bulb Size

The Audi TT back up light utilizes 921 and P21W bulb sizes for the rear illumination components. Data for the specific lighting requirements covers the period from 2000 through 2009.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2008-2015	921
2000-2006	P21W

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The Audi TT backup light specifications cover model years 2000-2015, with two distinct bulb types used across that span.
Model years 2008-2015 of the Audi TT use the 921 bulb, an ANSI-standard wedge-type (T15) rated at 12V and 16W.
The 921 is a wedge-base bulb, meaning it is held in its socket by the tension of the base itself rather than by a bayonet or screw mechanism.
Model years 2000-2006 use the P21W bulb, an ECE-standard single-filament signalling bulb rated at 12V and 21W.
The P21W uses a BA15s bayonet base, a single-contact fitting that locks into its socket with a quarter-turn.
The 921 and P21W are not interchangeable, as they differ in base type, wattage, and governing standard.
The P21W operates at 21W while the 921 operates at 16W, meaning the two bulbs draw different amounts of current even though both run on 12V systems.
The 921 follows the ANSI standard used in the United States and Canada, while the P21W follows the ECE standard used in Europe and other markets worldwide.