BMW 328i Back Up Light Bulb Size

The BMW 328i back up light utilizes H21W and P21W bulb sizes for the rear illumination system. Data for the specified lighting components covers the period from 1996 through 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
2016	H21W
2014-2015	P21W
1996-2000	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

Other Locations

Additional Notes

The BMW 328i uses two distinct bulb types across its model years for the back up light position: the P21W and the H21W, both operating at 12 volts and rated at 21 watts.
The P21W is the predominant back up light bulb across the 328i lineup, appearing in the 1996-2000 and 2014-2015 model years.
Both the P21W and H21W are single-filament signalling bulbs built to ECE standards, meaning they are designed for European and worldwide automotive applications rather than SAE-regulated North American markets.
Although the P21W and H21W share identical voltage and wattage ratings, they are not interchangeable due to different base types. The P21W uses a BA15s bayonet base, while the H21W uses a BAY9s base.
The BA15s base on the P21W is a single-contact bayonet fitting with a 15mm collar, a widely used base type in automotive signalling applications.
The BAY9s base on the H21W is an offset-pin bayonet fitting, a design that physically prevents incorrect installation of a non-equivalent bulb, making cross-substitution with a BA15s-based bulb mechanically impossible.
The 2016 BMW 328i shifted to the H21W with its BAY9s base, distinguishing it from all other listed model years, which use the BA15s-based P21W.