Porsche Cayenne inner tail light uses a P21/4W bulb size while outer tail light and standard tail light applications require a P21/5W bulb size. The replacement chart covers vehicle production years from 2003 to 2006 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 Porsche Cayenne uses two distinct bulb types across its tail light positions for the 2003-2006 model years: P21/4W in the inner tail light and P21/5W in the outer tail light.
Both the P21/4W and P21/5W are ECE-standard dual-filament bulbs, meaning each contains two separate filaments within a single envelope, allowing one bulb to serve two lighting functions simultaneously.
The P21/4W operates at 12 volts with filament ratings of 21 watts and 4 watts, while the P21/5W operates at 12 volts with filament ratings of 21 watts and 5 watts.
Although the wattage ratings of the P21/4W and P21/5W are similar, the two bulbs are not interchangeable due to differences in their base types.
The P21/4W uses a BAZ15d bayonet base, while the P21/5W uses a BAY15d bayonet base. These bases differ in the offset positioning of their locating pins, which physically prevents incorrect installation.
The BAZ15d base on the P21/4W features asymmetrically placed pins on different horizontal levels, ensuring the bulb can only be seated in one orientation within its socket.
The outer tail light position on the Porsche Cayenne calls for the P21/5W across all four model years covered in the specifications, with the same fitment applying to both listed outer tail light entries for each year.
The inner tail light position on the Porsche Cayenne requires the P21/4W for the full 2003-2006 range, a bulb type with a lower secondary filament output than the P21/5W used in the outer position.