The Smart Fortwo tail light utilizes a P21/5W bulb size for the rear illumination system. Data for the specified component covers the 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 P21/5W is the sole bulb type specified for the Smart Fortwo outer tail light across all listed model years.
The P21/5W is an ECE-standard dual-filament bulb, meaning it contains two separate filaments within a single glass envelope, one rated at 21 watts and one at 5 watts, allowing it to serve both a brighter signalling function and a dimmer running light function simultaneously.
The bulb operates on a 12-volt electrical system, which is standard for passenger vehicles in this class.
The P21/5W uses a BAY15d bayonet base, a two-pin offset base design. The offset pin placement is a deliberate anti-misorientation feature, ensuring the filaments are positioned correctly relative to the lamp housing.
The Smart Fortwo (2008-2016) is specified with the P21/5W for the outer tail light without any noted trim or package conditions.
For the 2016-2018 model years, the P21/5W fitment carries a "Without LED Tail Lights" condition, indicating that vehicles equipped with factory LED tail lights do not use this bulb type in that position.
The 2016 model year appears under both a conditional and an unconditional entry, reflecting a production period that spanned two distinct tail light configurations.
Because the BAY15d base uses offset pins, it is not interchangeable with the single-filament BA15s or the twin-filament BAY15d variants that carry different pin offsets, making base confirmation necessary before substitution.