The Audi RS4 front inner turn signal requires a PY21W bulb size, while front and rear turn signals use P21W bulbs. The replacement chart covers 2007 to 2008 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 Audi RS4 (2007-2008) uses two distinct bulb types across its turn signal positions: PY21W for the front inner turn signal and P21W for both the front and rear turn signals.
The P21W is an ECE-standard single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base. It appears in two separate positions on the RS4, covering the front and rear turn signals.
The PY21W is an ECE-standard single-filament amber bulb rated at 12V and 21W, fitted with a BAU15s bayonet base. Its amber tint is built into the glass envelope rather than the lens, which is the defining characteristic of this bulb type.
Although the P21W and PY21W share the same 12V, 21W electrical rating, their bases are not interchangeable. The BA15s base of the P21W has straight pins, while the BAU15s base of the PY21W has offset pins set at a 150-degree angle, physically preventing cross-installation between the two types.
The front inner turn signal position on the Audi RS4 (2007-2008) specifically requires the PY21W, meaning the amber coloration is produced by the bulb itself rather than by an amber-tinted housing or lens at that location.
Both bulb types conform to ECE regulations, which govern lighting standards across Europe and many other markets worldwide, indicating these specifications reflect internationally recognized performance and safety criteria.