BMW M5 Back Up Light Bulb Size

The BMW M5 back up light utilizes H21W, 921, and P21W bulb sizes depending on the specific version of the component required for the vehicle. Available data covers a range from 1988 through 2020 for the various configurations listed in the provided specifications.

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
2018-2020	H21W
2013-2016	921
2006-2010	921
2000-2003	P21W
1991-1993	P21W
1988	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BAY9s base. 12V, 21W.	H21W
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 BMW M5 backup light specifications reference three distinct bulb types across its model history: H21W, 921, and P21W.
The H21W is an ECE-standard single-filament signalling bulb rated at 12V and 21W, fitted with a BAY9s base. It is the specified backup light bulb for the BMW M5 for the 2018-2020 model years.
The P21W is also an ECE-standard single-filament signalling bulb rated at 12V and 21W, but it uses a BA15s bayonet base rather than the BAY9s base found on the H21W. Despite sharing the same voltage and wattage, the two bulbs are not interchangeable due to their different base types.
The P21W is the specified bulb for the 1988 and 1991-1993 model years, as well as the 2000-2003 model years.
The 921 is an ANSI-standard wedge-type bulb in the T15 form factor, rated at 12V and 16W. It draws less wattage than either the H21W or the P21W.
The 921 is the specified backup light bulb for the 2006-2010 and 2013-2016 model years.
The BAY9s base on the H21W and the BA15s base on the P21W are both bayonet-style fittings, but they are physically distinct and not mutually compatible.
The wedge-style base of the 921 bulb differs fundamentally from the bayonet bases used by both the H21W and the P21W, making cross-substitution between the 921 and either ECE-standard bulb mechanically incompatible.
The H21W and P21W share identical electrical ratings of 12V and 21W, yet their differing base configurations mean socket fitment determines which of the two applies to a given model year.