BMW M3 Back Up Light Bulb Size

The BMW M3 back up light utilizes H21W, P21W, and 921 bulb sizes depending on the specific production version. Available data for the lighting components spans from 1988 through 2018.

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
2017-2018	H21W
2015	P21W
2008-2013	921
2001-2006	P21W
1995-1999	P21W
1988-1991	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BAY9s base. 12V, 21W.	H21W
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921

Other Locations

Additional Notes

The BMW M3 back up light specifications reference three distinct bulb types across the model's history: the H21W, P21W, and 921.
The P21W is the most frequently specified bulb in these records, covering the BMW M3 across 1988-1991, 1995-2006, and 2015.
The P21W operates at 12V and 21W, uses a BA15s single-contact bayonet base, and conforms to ECE standards used in Europe and worldwide markets.
The H21W, specified for the 2017-2018 BMW M3, also operates at 12V and 21W under ECE standards but uses a BAY9s base, which is offset rather than centered, making it physically incompatible with BA15s sockets despite sharing the same wattage as the P21W.
The 921 is an ANSI-standard wedge-type bulb in the T15 form factor, rated at 12V and 16W, and was specified for the BMW M3 from 2008-2013.
The 921 draws 5 fewer watts than both the H21W and P21W, reflecting a lower power output for the back up light function during those model years.
The H21W and P21W share identical voltage and wattage ratings but are not interchangeable due to their different base types, BAY9s and BA15s respectively.
The 921 wedge base is mechanically incompatible with the bayonet sockets used by both the P21W and H21W, meaning no cross-substitution is possible among the three bulb types listed.