Mercedes-Benz CLA45 AMG Back Up Light Bulb Size

Additional Notes

• The 921 bulb is the back up light size for the Mercedes-Benz CLA45 AMG across the 2014-2019 model years, specifically on vehicles equipped with Halogen Capsule Headlamps.
• The 921 follows the ANSI standard, which governs bulb specifications in the US and Canada. It uses a wedge-style T15 base and operates at 12V with a 16W output.
• The PY21W is the back up light size for the 2020 model year CLA45 AMG. Unlike the 921, it carries no headlamp-related fitment condition in the specifications.
• The PY21W follows the ECE standard, which applies to Europe and worldwide markets. It uses a BAU15s bayonet base and operates at 12V with a 21W output.
• The BAU15s base of the PY21W is an offset bayonet fitting, which is physically distinct from the wedge base of the 921. These two bulb types are not interchangeable.
• The PY21W is an amber-tinted single-filament bulb, whereas the 921 is a clear wedge bulb. The difference in light color and base type reflects the separate regulatory standards each bulb is designed to satisfy.
• The 921 bulb draws 16W, while the PY21W draws 21W. Installing a higher-wattage bulb in a socket rated for a lower one can stress the wiring and socket over time.
• The fitment note "With Halogen Capsule Headlamps" on the 2014-2019 entries indicates that headlamp type is a determining factor in the correct back up light bulb size for those model years.