Mercedes-Benz GLK350 front turn signal bulbs use 12174NA, 3457NA, or 3357NA sizes, while rear turn signal bulbs use PY21W or 12496 sizes. The replacement chart covers 2010 to 2015 model 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 front turn signal uses three distinct bulb types across the 2010-2015 model years, with the 3357NA fitted in 2010-2011, the 3457NA in 2012, and the 12174NA in 2013-2015.
The 3357NA and 3457NA are both ANSI-standard T25 wedge bulbs rated at 12V with natural amber glass, though they differ in filament count. The 3357NA is a single-filament bulb rated at 27W, while the 3457NA is a dual-filament bulb rated at 27W and 7W.
The 12174NA is designated by an OEM part number rather than an ANSI or ECE standard number, and it carries a natural amber glass construction operating at 12V.
Because the 3357NA and 3457NA share the T25 wedge form factor and natural amber glass, physical fitment between the two is possible, but the difference in filament count means they are not functionally interchangeable in all applications.
The rear turn signal of the GLK350 uses the PY21W for model years 2011-2015. This bulb follows the ECE standard used in Europe and worldwide markets, featuring a BAU15s offset bayonet base, a single filament, and a rating of 12V at 21W.
The BAU15s base of the PY21W has an offset pin arrangement that physically prevents substitution with the more common BA15s base bulbs, making base compatibility a relevant factor when sourcing replacements.
The 2010 rear turn signal uses the 12496, a Philips/Osram part number designation for a 12V halogen bulb intended for specialty applications, which differs from the PY21W used in all subsequent model years.
The front and rear turn signal positions on the GLK350 do not share a common bulb type in any single model year, as the front positions use ANSI or OEM-numbered wedge bulbs while the rear positions use ECE or specialty halogen types.