The BMW 428i uses a PY24WNA bulb size for the front turn signal and a P21W bulb size for the rear turn signal. The replacement chart covers 2014 to 2016 model years with corresponding bulb specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW 428i uses two distinct bulb types across its front and rear turn signal positions for the 2014-2016 model years: the PY24WNA at the front and the P21W at the rear.
The PY24WNA is an ANSI-standard bulb intended for the US and Canadian markets. It operates at 12V and draws 24W, with an amber-tinted envelope and a PGU20-4 base.
The PGU20-4 base is a wedge-pin type specific to the PY24WNA family, which means it is not interchangeable with bulbs that use a standard bayonet or wedge base.
The PY24WNA is functionally an amber-producing variant of the ECE-standard PY24W. The amber coloring is built into the bulb itself rather than produced by a colored lens.
The front turn signal fitment of the BMW 428i specifies the PY24WNA exclusively for vehicles equipped with HID headlamps across all three model years covered.
The P21W is an ECE-standard single-filament bulb operating at 12V and 21W. Its BA15s bayonet base is a single-contact fitting, distinguishing it from the dual-contact BA15d base used in some other P21-series bulbs.
The P21W designation indicates a single filament, which means the bulb serves one signalling function only and is not a combined stop and turn unit.
The rear turn signal position on the 428i uses the P21W across the full 2014-2016 span, making it consistent regardless of headlamp type.
Because the PY24WNA and P21W use different base types, PGU20-4 and BA15s respectively, the two bulbs are not interchangeable between the front and rear positions.