BMW M2 front turn signal uses PY21W bulb size while rear turn signal requires 7440 or P21W bulb size. The replacement bulb chart covers 2016 to 2020 production years.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW M2 front turn signal uses the PY21W bulb across the 2016-2018 model years.
PY21W is an ECE-standard single-filament amber bulb rated at 12V and 21W, fitted with a BAU15s bayonet base.
The amber tint of the PY21W is built into the bulb itself, which is a defining characteristic of this ECE type and distinguishes it from clear-glass signalling bulbs that rely on a colored lens.
The rear turn signal on the BMW M2 uses the P21W bulb for the 2016-2018 model years and transitions to the 7440 for 2019-2020.
P21W is an ECE-standard single-filament bulb rated at 12V and 21W, fitted with a BA15s bayonet base.
The BAU15s base of the PY21W and the BA15s base of the P21W are not interchangeable. Although both are bayonet-style bases of the same 15mm width, the BAU15s has offset pins at 150 degrees, while the BA15s has aligned pins, making physical substitution between the two impossible without modification.
The 7440 is an ANSI-standard single-filament bulb in a T20 wedge form, rated at 12V and 21W, and is the North American market counterpart to similar wattage ECE signalling bulbs.
The wedge base of the 7440 is mechanically incompatible with the bayonet bases used by the PY21W and P21W, so these bulb types cannot be substituted for one another regardless of matching voltage and wattage ratings.
All three bulb types listed across these specifications share the same 12V operating voltage and 21W power rating, though their base types and regulatory standards differ.
The shift from P21W to 7440 in the rear turn signal between the 2018 and 2019 model years reflects a change in base type from a bayonet fitting to a wedge fitting, which affects socket compatibility in the housing.