Audi A8 Back Up Light Bulb Size

The Audi A8 back up light bulb size specifications include 12177, 12184, and 921 bulb configurations for this vehicle model. The replacement chart covers 1997 through 2013 production years with corresponding bulb size data.

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
2011-2013	12177
2009-2010	12184
2004-2008	921
1997-2003	P21W

Bulb Specifications

Description	Bulb Size
Philips part number. Halogen bulb, specialty application. 12V.	12177
Philips part number. Halogen bulb, specialty application. 12V.	12184
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 A8 backup light specifications span model years 1997 through 2013 and reference four distinct bulb sizes across that period.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base. It is the bulb type covering the longest consecutive stretch in these specifications, appearing across the 1997-2003 model years of the Audi A8.
The BA15s bayonet base on the P21W is a single-contact fitting, meaning it is not interchangeable with dual-contact bayonet bulbs despite sharing a similar physical form.
The 921 is an ANSI-standard wedge bulb of the T15 type, rated at 12V and 16W. It is specified for the Audi A8 across the 2004-2008 model years.
The P21W and the 921 are not interchangeable. The P21W uses a bayonet base while the 921 uses a wedge base, and the two standards originate from different regional regulatory frameworks.
Bulb sizes 12177 and 12184 are Philips part numbers rather than ANSI or ECE standard designations, classifying them as specialty halogen bulbs rated at 12V.
The 12184 is specified for the 2009-2010 model years, while the 12177 is specified for the 2011-2013 model years. Although both are Philips specialty halogen bulbs at 12V, they carry different part numbers and are not confirmed as interchangeable by these specifications.
The transition from the ANSI 921 wedge bulb to the Philips 12184 specialty bulb between the 2008 and 2009 Audi A8 represents a base-type change, which affects physical fitment in the socket.