BMW ActiveHybrid 3 front turn signal bulbs use PY21W size while rear turn signal bulbs use P21W size. The replacement chart covers 2013 through 2015 vehicle production years with corresponding bulb size specifications.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The BMW ActiveHybrid 3 uses two distinct bulb types across its turn signal positions: PY21W for the front and P21W for the rear, a split that applies uniformly across the 2013-2015 model years covered in the specifications.
PY21W is an ECE-standard single-filament amber bulb rated at 12V and 21W, mounted on a BAU15s bayonet base. The amber coloring is built into the glass envelope itself, meaning the bulb produces a yellow signal output without relying on a colored lens.
P21W is also an ECE-standard single-filament bulb rated at 12V and 21W, but it uses a BA15s bayonet base and produces a clear or white light output, with signal color determined by the lens housing rather than the bulb itself.
Although PY21W and P21W share the same 12V, 21W electrical rating, they are not interchangeable. The BAU15s base of the PY21W has offset pins positioned at an angle, while the BA15s base of the P21W has straight offset pins, making physical installation in the wrong socket impossible under normal conditions.
The base difference between BAU15s and BA15s serves as a deliberate anti-substitution measure in ECE-compliant vehicles, preventing a clear P21W bulb from being installed in a front turn signal position that requires the inherent amber output of a PY21W.
Both bulb types conform to ECE regulations, which govern lighting standards across Europe and a broad range of international markets, reflecting the ActiveHybrid 3's design compliance with those regional requirements.
At 21W, both bulbs fall within the traditional incandescent power range for automotive signalling applications, a wattage associated with the flash rate compatibility requirements of standard thermal or electronic flasher relay units.