BMW M4 front turn signal uses PY24WNA bulb size while rear turn signal requires P21W bulb size. Replacement chart covers 2015 to 2018 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 M4 uses two distinct bulb types across its front and rear turn signal positions for the 2015-2018 model years: PY24WNA for the front and P21W for the rear.
The PY24WNA is an ANSI-standard bulb used in the United States and Canada. It operates at 12V and 24W, features a PGU20-4 base, and is the amber variant of the ECE-standard PY24W.
Because the PY24WNA and PY24W share a similar designation but differ in regional standard, they are not directly interchangeable. The PGU20-4 base is specific to the ANSI version, and substituting the ECE variant may result in an improper fit or non-compliance with regional regulations.
The front turn signal position on the BMW M4 specifies the PY24WNA exclusively for configurations with HID headlamps across all four model years covered.
The P21W is an ECE-standard single-filament bulb rated at 12V and 21W. It uses a BA15s bayonet base, which is a single-contact bayonet mount with a 15mm collar.
The BA15s base on the P21W is a single-filament fitting, meaning it is not interchangeable with visually similar bayonet bulbs such as the BAY15d, which carries two filaments and offset pins.
The P21W rear turn signal fitment remains consistent across the 2015-2018 model years, indicating no change in rear signal socket design during that production span.
The PY24WNA front turn signal fitment is also consistent across the 2015-2018 model years, tied in each case to the HID headlamp configuration.