BMW 525i Back Up Light Bulb Size

The BMW 525i back up light utilizes bulb sizes 921 and P21W depending on the specific version of the vehicle. Available data for the lighting components covers the range from 1989 through 2007.

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
2004-2007	921
2001-2003	P21W
1989-1995	P21W

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The BMW 525i backup light specifications reference two distinct bulb types across its model years: the 921 and the P21W.
The 921 is an ANSI-standard wedge bulb of the T15 form factor, rated at 12V and 16W, and is the designated backup light bulb for the 2004-2007 BMW 525i.
The T15 wedge base on the 921 bulb connects by inserting directly into a socket without a separate locking mechanism, which is a defining characteristic of the wedge bulb family.
The P21W follows the ECE standard, which governs lighting regulations across Europe and much of the wider international market, and is rated at 12V and 21W.
The P21W uses a BA15s bayonet base, a single-contact fitting that locks into its socket with a quarter-turn motion, distinguishing it physically from the wedge-type 921.
The BMW 525i carries the P21W specification across the 1989-1995 and 2001-2003 model years for its backup light position.
The 921 and P21W are not interchangeable. Their base types are mechanically incompatible, and the P21W draws 21W versus the 921's 16W, reflecting a difference in electrical load.
The shift from P21W to the 921 between the 2003 and 2004 BMW 525i represents a change in both the bulb standard and the socket type, meaning the two generations of this vehicle require physically different replacement bulbs for the backup light position.