Mercedes-Benz E320 Back Up Light Bulb Size

The Mercedes-Benz E320 back up light utilizes 921 and P21W bulb sizes for the lighting components. Available data for the specified vehicle covers the range from 1994 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
2008-2009	921
1994-2003	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 Mercedes-Benz E320 backup light specifications cover model years 1994-2003 and 2008-2009, with two distinct bulb types appearing across those years.
The P21W bulb is specified for the E320 across the 1994-2003 model years, making it the more widely represented bulb type in these specifications.
The 921 bulb is specified for the 2008-2009 E320 model years.
The P21W operates under the ECE standard, which governs lighting equipment regulations in Europe and much of the world, while the 921 operates under the ANSI standard used in the United States and Canada.
Both bulbs share the same operating voltage of 12V, which is standard for automotive electrical systems.
The P21W draws 21 watts, while the 921 draws 16 watts, meaning the two bulb types are not electrically equivalent despite sharing the same voltage rating.
The P21W uses a BA15s bayonet base, a single-contact fitting that locks into place with a twist, whereas the 921 is a wedge-type bulb that is held in place by tension from its socket rather than a locking mechanism.
The P21W is classified as a single-filament signalling bulb, a construction that suits on/off functions such as reverse lighting rather than variable-intensity applications.
The 921 is a T15 wedge bulb, a designation that refers to its tubular glass envelope and wedge base form factor as defined by ANSI standards.
The differing base types between the P21W and the 921 mean the two bulbs are not physically interchangeable, as each requires a socket designed specifically for its respective fitting.