Mercedes-Benz GLK350 front fog light bulbs use H11 size while rear fog light bulbs use P21W size. The replacement chart covers 2010 to 2012 vehicle production years 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 GLK350 uses the H11 bulb for the front fog light position across the 2010-2012 model years.
The H11 is a single-filament halogen bulb operating at 12V and 55W, fitted with a PGJ19-2 base, and rated under the ECE standard used in Europe and worldwide, with additional approval for use in the United States.
The rear fog light position on the GLK350 uses the P21W bulb across the 2010-2012 model years.
The P21W is a single-filament signalling bulb rated at 12V and 21W, fitted with a BA15s bayonet base, and also governed by the ECE standard.
The BA15s base on the P21W is a single-contact bayonet fitting, which is physically distinct from the PGJ19-2 wedge-style base on the H11, making the two bulb types non-interchangeable with each other.
The H11 draws 55W while the P21W draws 21W, reflecting their respective roles as a high-output forward lighting source and a lower-power signalling lamp.
Both bulb types operate on a 12V electrical system, consistent with standard automotive voltage.
The single-filament construction of the H11 means it serves one lighting function only and is not a dual-purpose bulb shared with another circuit such as a low beam or turn signal.
The P21W designation follows ECE naming conventions in which the letter P indicates a single-contact bayonet cap, 21 indicates the wattage, and W indicates a clear glass envelope.