The BMW 320i brake light uses H21W and P21W bulb sizes for the lighting components. Data for the specific bulb requirements covers the time periods from 1977 to 1983 and 2013 to 2018.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 320i brake bulb specifications reference two bulb types across all listed model years: the H21W and the P21W. Both operate at 12V and 21W, and both are single-filament signalling bulbs built to the ECE standard used in Europe and worldwide.
Although the H21W and P21W share identical voltage and wattage ratings, they are not interchangeable. The H21W uses a BAY9s base, while the P21W uses a BA15s bayonet base. These are physically distinct fittings.
The H21W appears as the brake bulb for the BMW 320i across the 2013-2018 model years, with the single exception of 2014, which specifies the P21W instead.
The 2014 BMW 320i is the only year within the 2013-2018 range to specify the P21W for the general brake position rather than the H21W, making it a notable fitment exception within that generation.
All listed model years from 1977-1983 specify the P21W for the brake position, with no adaptive designation noted for those entries.
The adaptive designation appears alongside bulb specifications for the 2013-2018 model years, indicating that the brake lighting system in those vehicles incorporates adaptive functionality beyond a standard fixed brake light.
For the 2013-2015 model years, the specifications distinguish between an inner brake and an outer brake position. The inner brake position uses the H21W across all three of those years, while the outer brake position uses the P21W across the same years.
The split between inner and outer brake positions in the 2013-2015 BMW 320i means both the H21W and P21W base types are present simultaneously in the same vehicle, requiring attention to position when sourcing replacement bulbs.