Mercedes-Benz CLA250 Back Up Light Bulb Size

The Mercedes-Benz CLA250 back up light utilizes 921 and PY21W bulb sizes for the specified lighting components. Data for the provided bulb sizes covers the range from 2014 to 2020.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Bulb Size by Year Range

Years	Bulb Size
2020	PY21W
2014-2019	921 (With Halogen Capsule Headlamps)

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament amber bulb with BAU15s bayonet base. 12V, 21W.	PY21W
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921

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Additional Notes

The 921 bulb is the back up light size for the Mercedes-Benz CLA250 across the 2014-2019 model years, all of which carry the fitment note "With Halogen Capsule Headlamps."
The 921 follows the ANSI standard used in the US and Canada. It is a T15 wedge bulb rated at 12V and 16W.
The 2020 Mercedes-Benz CLA250 uses a different bulb entirely, the PY21W, rather than the 921 found in earlier model years.
The PY21W follows the ECE standard used in Europe and worldwide. It is a single-filament amber bulb with a BAU15s bayonet base, rated at 12V and 21W.
The BAU15s bayonet base of the PY21W is offset, meaning it is not interchangeable with bulbs that use a standard BA15s base, even though the physical size may appear similar.
The 921 uses a wedge base, while the PY21W uses a BAU15s bayonet base. These two base types are mechanically incompatible, so the 2020 socket will not accept a 921 bulb.
The wattage difference between the two bulbs is notable. The PY21W draws 21W versus the 921 at 16W, which reflects the differing power demands of each standard.
The amber tint of the PY21W is built into the bulb itself rather than the lens, which is a characteristic of ECE-compliant amber signaling bulbs.