The Audi A6 tail light utilizes 12961, P21W, and P21/5W bulb sizes for the rear lighting components. Available data for the specified vehicle covers the range from 1995 through 2014.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The P21/5W is the most frequently specified bulb across the Audi A6 tail light data, appearing in both the outer tail light and a second tail light position across model years spanning 1995-2006. It follows the ECE standard and carries a dual-filament design rated at 12V with outputs of 21W and 5W, mounted on a BAY15d offset-pin bayonet base.
The P21W shares the same ECE standard origin and BA15s bayonet base as the P21/5W but carries only a single filament rated at 21W. The two bulbs are not interchangeable despite their similar appearance, as the BAY15d base of the P21/5W uses offset pins specifically to prevent incorrect installation.
The Philips part numbers 12821 and 12961 both describe a T10 miniature wedge bulb with a W2.1x9.5d base, rated at 12V and 5W. These two part numbers are functionally equivalent in electrical and physical terms.
The 12821 is specified for the Audi A6 inner tail light across the 1995-1997 model years, making it the sole bulb type listed for that position in the available data.
The outer tail light position on the Audi A6 transitions through three distinct bulb types across its model year range. The 1995-1997 years use P21W, the 1998-2006 years shift to P21/5W, and the 2007-2011 years return to P21W.
A second outer tail light position on the Audi A6 also spans multiple bulb types. The 1995-1997 years use P21W, the 1998-2006 years use P21/5W, the 2007-2008 years use P21W, and the 2009-2014 years use the Philips 12961 wedge bulb.
The shift to the Philips 12961 wedge bulb in the 2009-2014 outer tail light position represents a significant change in base type, moving from a bayonet-style mount to a wedge-style W2.1x9.5d base, which means earlier bayonet-based bulbs are not physically compatible with sockets designed for the wedge format.