Mercedes-Benz GL450 Back Up Light Bulb Size

The Mercedes-Benz GL450 back up light uses 921 and P21W bulb sizes depending on the specific version of the vehicle. Available data for the lighting components covers the range from 2007 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
2007-2012	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 GL450 backup light specifications cover model years 2007-2016 and reference two distinct bulb types: the 921 and the P21W.
The 921 bulb follows the ANSI standard, which governs automotive lighting in the United States and Canada. It is a T15 wedge-base bulb rated at 12 volts and 16 watts.
The P21W bulb follows the ECE standard, the regulatory framework used in Europe and much of the rest of the world. It is a single-filament signalling bulb rated at 12 volts and 21 watts, mounted via a BA15s bayonet base.
The BA15s bayonet base of the P21W is a single-contact fitting, which is mechanically distinct from wedge-base sockets. The two bulb types are not interchangeable due to their differing base designs.
The 921 and P21W also differ in wattage. The P21W draws 21 watts, while the 921 draws 16 watts, meaning the two bulbs are not electrically equivalent even at the same 12-volt operating voltage.
The GL450 (2013-2016) uses the 921 bulb for the backup light position.
The GL450 (2007-2012) uses the P21W bulb for the backup light position.
The transition between bulb types coincides with a model year change between 2012 and 2013, indicating a difference in socket design between those two production periods that makes cross-year substitution incompatible.