Mercedes-Benz S400 Back Up Light Bulb Size

The Mercedes-Benz S400 back up light requires a bulb size of 921 for the rear lighting assembly. Data for the specified component covers the range from 2010 to 2013.

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
2010-2013	921

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921

Other Locations

Additional Notes

The Mercedes-Benz S400 uses the 921 bulb for the back up light across the 2010-2013 model years.
The 921 is a T15 wedge-base bulb, meaning it connects to its socket through a plastic wedge-shaped base rather than a bayonet or screw fitting.
The 921 bulb operates at 12 volts and draws 16 watts, which is consistent with standard automotive incandescent back up light applications.
The 921 follows the ANSI standard, a classification system recognized in both the United States and Canada, indicating a standardized specification for physical and electrical properties.
The T15 designation refers to the tubular envelope size of the bulb, with the numeric portion indicating the width in eighths of an inch, placing it in a relatively compact form factor common to back up and interior lighting positions.
Because the 921 is an ANSI-standardized wedge bulb, it is produced by multiple manufacturers, though fitment suitability depends on the bulb meeting the 12V, 16W electrical specification.