The Mercedes-Benz C350e uses a 12174NA bulb size for the front turn signal and a PY21W bulb size for the rear turn signal. The replacement chart covers vehicle production years spanning 2016 to 2018 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 Mercedes-Benz C350e uses two distinct bulb types across its turn signal positions: the 12174NA for the front and the PY21W for the rear, both rated at 12 volts.
Both bulb types apply uniformly to the 2016-2018 model years, and both are specified exclusively for vehicles equipped with Halogen Capsule Headlamps.
The 12174NA is an OEM part number designation rather than an industry-standard code, and it refers to a natural amber glass variant, meaning the amber color is produced by the glass envelope itself rather than by a coating or the lens.
The PY21W follows the ECE (Economic Commission for Europe) lighting standard, which is used across European and worldwide markets, distinguishing it from SAE-standard bulbs more common in North American applications.
The PY21W is a single-filament bulb, meaning it serves one lighting function only, which in this context is the rear turn signal.
The PY21W uses a BAU15s bayonet base, which features offset pins to prevent incorrect installation. The offset base differentiates it from the more common BA15s base, and the two are not physically interchangeable.
The PY21W operates at 21 watts, a wattage level associated with sufficient luminous intensity to meet turn signal visibility requirements under ECE regulations.
Because the 12174NA is identified by an OEM part number, substitution with aftermarket equivalents requires confirmation that the replacement matches the natural amber glass construction and 12-volt rating.