The BMW X3 brake component utilizes P21W, H21W, and 921 bulb sizes for various lighting applications. Available data for the specified vehicle covers the period from 2004 through 2020.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW X3 brake light specifications reference three bulb types across the model's production range: P21W, H21W, and 921. The P21W and H21W are both ECE-standard single-filament signalling bulbs rated at 12V and 21W, while the 921 is an ANSI-standard wedge bulb rated at 12V and 16W.
The P21W uses a BA15s bayonet base, and the H21W uses a BAY9s base. Although both bulbs share the same 12V/21W electrical rating, their bases are physically different and the two types are not interchangeable with each other.
The 921 is a T15 wedge bulb operating at 16W, which is a lower wattage than both the P21W and H21W. Its ANSI-standard wedge fitting is incompatible with the bayonet and BAY9s bases used by the ECE bulbs.
The BMW X3 (2004-2006 and 2020) uses a P21W for the brake light position without any adaptive designation, indicating a standard fitment for those model years.
The adaptive designation appears across multiple model years in the main brake position, specifically for P21W fitments in 2011, 2013, 2015-2016, 2018-2019, and for H21W fitments in 2012, 2014, and 2017. This designation signals that the vehicle's lighting system includes adaptive functionality, which may affect bulb replacement compatibility beyond the base bulb type alone.
The 921 wedge bulb is specified for the main brake position in 2007-2010, and also appears in the outer brake sub-position for 2007-2010. This makes it the only bulb type to recur across both a main and a sub-position within the same model years.
The inner brake sub-position for 2007-2017 exclusively uses the H21W with its BAY9s base, with no variation across those years. This sub-position does not reference the adaptive designation that appears in the main brake position for some of the same years.
In 2017, the main brake position specifies an H21W (Adaptive), while the inner brake sub-position also specifies an H21W and the outer brake sub-position specifies a P21W. That single year therefore requires two different ECE bulb base types across its brake light positions.
For 2007-2010, the outer brake sub-position uses the 921 wedge bulb, while the inner brake sub-position for those same years uses the H21W. Replacing bulbs in those model years requires sourcing two physically incompatible bulb types for the brake light assembly alone.
The P21W is the most frequently specified bulb type across the full set of brake light positions in these specifications, appearing in the main brake position across the widest span of model years and carrying the adaptive designation in the majority of those instances.