The BMW 128i brake light utilizes P21W and H21W bulb sizes according to the provided technical specifications for the lighting system. Data for the lighting components covers the range from 2008 to 2013.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 128i uses two bulb types across its brake light positions: P21W and H21W. Both operate at 12V and 21W, and both carry ECE certification for use in Europe and worldwide markets.
Despite sharing identical voltage and wattage ratings, P21W and H21W are not interchangeable. The P21W uses a BA15s bayonet base, while the H21W uses a BAY9s base, making the two physically incompatible with each other's sockets.
The inner brake position on the BMW 128i uses the H21W bulb across all model years from 2008-2013, with no variation throughout the production run.
The outer brake position on the BMW 128i uses the P21W bulb across all model years from 2008-2013, also without variation.
The general brake light position carries an "Adaptive" designation for all model years from 2008-2013, indicating the vehicle uses an adaptive brake light system in that position.
Within the adaptive brake position, the BMW 128i used the H21W in 2008, 2009, and 2011, while the P21W was specified for 2010, 2012, and 2013.
The BA15s base of the P21W is a single-contact bayonet fitting, a widely used base type in automotive signalling applications. The BAY9s base of the H21W is an offset-pin bayonet fitting, which physically prevents incorrect installation in a BA15s socket.