The BMW 330i front side marker bulb uses a 12961 size with P21/5W specification, while the rear side marker bulb uses a P21/4W size. The replacement chart covers 2001 to 2006 model 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 330i front side marker uses the 12961 bulb for model years 2002-2006. This is a Philips part number referencing a miniature wedge-type T10 bulb with a W2.1x9.5d base, rated at 12V and 5W.
The 2001 BMW 330i front side marker uses a P21/5W bulb rather than the 12961 found in later model years, indicating a fitment difference between the 2001 model year and the 2002-2006 range.
The P21/5W is an ECE-standard dual-filament bulb with a BAY15d bayonet base, rated at 12V with filaments drawing 21W and 5W respectively. Its dual-filament design distinguishes it from the single-filament T10 used in later front side marker positions.
The rear side marker on the BMW 330i uses the P21/4W bulb for model years 2001-2003. This is an ECE-standard dual-filament bulb rated at 12V, with filaments drawing 21W and 4W.
The P21/4W uses a BAZ15d bayonet base, while the P21/5W uses a BAY15d bayonet base. These two base types are not interchangeable despite the similar bulb designations, as the offset pin positions differ between BAZ15d and BAY15d fittings.
The T10 wedge base (W2.1x9.5d) used by the 12961 bulb is physically incompatible with the bayonet bases of the P21/5W and P21/4W, meaning no cross-substitution is possible between the front side marker bulb of 2002-2006 models and those used in the 2001 model year.