Mercedes-Benz GLA250 front fog light uses H11 bulb size while rear fog light requires H21W bulb size. The chart covers 2015 to 2020 model years with replacement 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 GLA250 front fog lights use the H11 bulb across the 2015-2020 model years.
The H11 is a single-filament halogen bulb operating at 12V and 55W, built to the ECE standard recognized in Europe and worldwide, with additional approval for use in the United States.
The H11 bulb uses a PGJ19-2 base, a proprietary locking connector that is not interchangeable with other common halogen bases such as H9 or H8, despite those bulbs sharing a similar physical form.
The GLA250 rear fog lights use the H21W bulb across the 2015-2019 model years.
The H21W is a single-filament signalling bulb rated at 12V and 21W, also built to the ECE standard.
The H21W uses a BAY9s base, an offset bayonet fitting designed to prevent incorrect installation of bulbs with different wattage ratings in the same housing.
The front and rear fog lights on the GLA250 use entirely different bulb families, H11 and H21W respectively, and the two are not interchangeable in any capacity.
The lower wattage of the H21W (21W) compared to the H11 (55W) reflects its role as a signalling bulb rather than an illumination source, as rear fog lights are intended to increase vehicle visibility to following traffic rather than to project light onto the road.