Mercedes-Benz CLS550 front fog light bulbs use H7 and H11 sizes, while rear fog light bulbs use 921 size. The replacement chart covers 2007 to 2011 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 CLS550 front fog light uses the H7 bulb for 2007-2009 and 2011, while the 2010 model year uses the H11 bulb instead.
The H7 is an ECE-standard single-filament halogen bulb rated at 12V and 55W, fitted with a PX26d base, and carries approval in the US and Japan in addition to European and worldwide markets.
The H11 is also an ECE-standard single-filament halogen bulb rated at 12V and 55W, but it uses a PGJ19-2 base, which is physically incompatible with the PX26d socket required by the H7.
Because the H7 and H11 use different base types, the two bulbs are not interchangeable, making the 2010 model year front fog light fitment distinct from all other years listed in the specifications.
Both the H7 and H11 share the same voltage and wattage ratings of 12V and 55W, meaning the electrical load on the fog light circuit is consistent across all listed model years despite the base difference.
The rear fog light on the CLS550 uses the 921 bulb across all listed model years from 2007-2011, indicating a consistent fitment for that position throughout the entire specification range.
The 921 is an ANSI-standard wedge-type bulb in the T15 form factor, rated at 12V and 16W, a significantly lower wattage than the halogen bulbs used in the front fog lights.
The 921 wedge bulb follows US and Canadian standards, whereas the H7 and H11 front fog bulbs follow ECE standards, reflecting a mixed regulatory framework within the same vehicle's lighting system.