The Smart Fortwo brake light requires a P21/5W bulb size for proper installation and function within the rear lighting assembly. Data for the specified component covers a range from 2008 through 2018.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Smart Fortwo uses the P21/5W bulb for its brake lights across the 2008-2018 model years.
The P21/5W is a dual-filament bulb rated at 12V with a 21W brake filament and a 5W running light filament, mounted on a BAY15d bayonet base. The offset pins of the BAY15d base ensure the bulb can only be inserted in one orientation, preventing filament misassignment.
The P21/5W follows the ECE standard, which is the regulatory framework used in Europe and much of the world outside North America.
For the 2016-2018 Smart Fortwo, the P21/5W brake bulb specification carries a "Without LED Tail Lights" qualifier, indicating that this bulb applies only to vehicles not equipped with the LED tail light package.
The center high mount stop light on the Smart Fortwo uses the 921 bulb across the 2008-2018 model years, with the exception of 2017, for which no center high mount stop light entry is listed in the specifications.
The 921 is a single-filament wedge-type bulb in the T15 form factor, rated at 12V and 16W, and follows the ANSI standard used in the United States and Canada.
The P21/5W and 921 bulbs are not interchangeable. They differ in base type, filament count, wattage, and the standards under which they are classified, making cross-substitution between the brake light and center high mount stop light positions incompatible.