Mercedes-Benz GL350 Back Up Light Bulb Size

The Mercedes-Benz GL350 back up light utilizes 921 and P21W bulb sizes for the rear illumination system. Data for the specified lighting components covers the range from 2010 to 2016.

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
2013-2016	921
2010-2012	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 GL350 backup light specifications cover model years 2010-2016, with two distinct bulb types used across that span.
The 921 bulb follows the ANSI standard, which is the regulatory framework used in the United States and Canada, while the P21W follows the ECE standard, which governs lighting equipment in Europe and most of the world.
The 921 is a wedge-type bulb in the T15 form factor, meaning it uses a plastic wedge base rather than a metal socket pin or bayonet fitting.
The P21W uses a BA15s bayonet base, a single-pin bayonet mount that locks into its socket with a twist, and it is rated as a single-filament signalling bulb.
The 921 operates at 12V and draws 16W, while the P21W operates at 12V but draws 21W, a difference of 5W between the two bulb types.
The Mercedes-Benz GL350 (2013-2016) specifies the 921 bulb for the backup light position.
The 2010-2012 model years specify the P21W, which is physically and electrically incompatible with the 921 due to differing base types and wattage ratings.
Because the 921 uses a wedge base and the P21W uses a bayonet base, the two bulbs are not interchangeable without modification to the socket.