The P21W is the sole bulb type listed across all brake light positions in the BMW X2 specifications, covering both the standard brake lights and the Center High Mount Stop Light.
The P21W operates at 12 volts with a 21-watt output and uses a BA15s single-contact bayonet base, which features a single filament dedicated to signalling functions rather than combined stop and tail duties.
As an ECE-rated bulb, the P21W conforms to European and international lighting standards, reflecting its widespread use in vehicles produced for global markets.
The BA15s bayonet base designation indicates a 15mm base with a single locating pin, a detail relevant to fitment, as it is not interchangeable with the BA15d base found on dual-filament bulbs of similar physical form.
The standard brake lights of the BMW X2 use the P21W across the 2018-2023 model years.
The Center High Mount Stop Light of the BMW X2 also specifies the P21W for the 2021-2023 model years, sharing the same bulb type as the main brake lights during that period.