BMW 640i Gran Coupe Back Up Light Bulb Size

The BMW 640i Gran Coupe back up light requires a 921 bulb size for the rear lighting assembly. Data for the specified vehicle covers the period from 2013 through 2018.

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
2013-2018	921

Bulb Specifications

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

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Additional Notes

The 921 is the bulb size specified for the back up light across all listed model years of the BMW 640i Gran Coupe, covering 2013-2018.
The 921 bulb follows the ANSI standard, which is the recognized classification system for automotive bulbs in the United States and Canada.
It uses a wedge-style base, designated T15, which means the bulb is held in place by friction rather than a twist-lock or bayonet mechanism.
The T15 designation refers to the bulb's body width expressed in eighths of an inch, placing it in a mid-range size category among wedge-type automotive bulbs.
The 921 operates at 12 volts, consistent with the standard electrical system voltage found in passenger vehicles.
Its rated wattage is 16W, which places it at a slightly higher output than the closely related 194 and 168 wedge bulbs, making direct substitution with lower-wattage wedge types inadvisable without confirming socket compatibility.
The wedge base format of the 921 is shared with several other ANSI-coded bulbs, though wattage and voltage ratings differ across those types, meaning physical fitment alone does not confirm electrical interchangeability.