BMW X3 Back Up Light Bulb Size

The BMW X3 back up light utilizes H21W, 921, and P21W bulb sizes depending on the specific version of the vehicle. Available information covers a range of years from 2004 through 2020.

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
2018-2020	H21W
2007-2017	921
2004-2006	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BAY9s base. 12V, 21W.	H21W
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 X3 backup light specifications cover model years 2004-2020 and reference three distinct bulb types across that span: the H21W, the 921, and the P21W.
The H21W and P21W are both ECE-standard bulbs rated at 12V and 21W, making them common in European and worldwide automotive applications. Despite sharing the same voltage and wattage, they are not interchangeable because they use different bases.
The H21W uses a BAY9s base, which features offset pins to ensure correct orientation during installation. The P21W uses a BA15s bayonet base, a single-contact design with symmetrical pins.
The 921 is an ANSI-standard wedge-type bulb classified as T15, operating at 12V and 16W. Its wedge construction requires no separate base or locking mechanism, as the glass envelope itself secures the bulb in the socket.
At 16W, the 921 draws less power than either the H21W or P21W, both of which operate at 21W. This difference means the bulb types are not electrically equivalent and are not substitutes for one another.
The BMW X3 (2004-2006) used the P21W for its backup light, representing the ECE bayonet-base format during that production period.
Starting with the 2007 model year, the X3 shifted to the 921 wedge bulb, a format that remained in use through the 2017 model year.
From 2018-2020, the X3 specification changed again to the H21W, returning to an ECE-standard single-filament bulb but with the BAY9s offset-pin base rather than the BA15s base used in earlier years.
Because the H21W and P21W share wattage and voltage ratings but differ in base type, physical fitment prevents accidental cross-installation between those two ECE bulbs.
The transition from the 921 wedge format to the H21W bayonet-pin format at the 2017-2018 model year boundary represents a socket-level change, meaning parts sourced for pre-2018 X3 models are physically incompatible with 2018-2020 housings.