Scion xB Back Up Light Bulb Size

The Scion xB back up light utilizes 921 and 7440 bulb sizes for the lighting components. Data for the specific bulb sizes covers the range from 2004 through 2015.

The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.

Back Up Light

Years	US Type	EU Type	Shop
2011-2015	921	W16W	Check Price
2008-2010	7440	W21W	Check Price
2004-2006	7440	W21W	Check Price

Outer Back Up Light

If US Type and EU Type show the same value, a direct cross-reference for this bulb is not available or the data is insufficient.

Years	US Type	EU Type	Shop
2015	7440	W21W	Check Price
2012-2014	921	W16W	Check Price
2011	7440	W21W	Check Price
2010	3057 (From 03/2010)	3057	Check Price
2010	7440 (To 03/2010)	W21W	Check Price
2009	7440 (Lower)	W21W	Check Price
2008	7440	W21W	Check Price
2004-2006	7440	W21W	Check Price

Bulb Specifications

Description	Type	Shop
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921	Check Price
ANSI standard (US & Canada). Single-filament wedge bulb (T20). 12V, 21W.	7440	Check Price
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3057	Check Price

Other Locations

Additional Notes

The 921 bulb is an ANSI-standard T15 wedge type rated at 12V and 16W, while the 7440 is an ANSI-standard T20 single-filament wedge type rated at 12V and 21W. The 3057 is an ANSI-standard T25 dual-filament wedge type rated at 12V with a 27W/7W output split across its two filaments.
The Scion xB back up light uses the 921 bulb for model years 2011-2015, and the 7440 bulb for model years 2004-2010, representing a difference of 5W between the two types.
The outer back up light position introduces additional variation. The 2015 model year uses a 7440 in that position, while the 2011-2014 range splits between the 7440 (2011) and the 921 (2012-2014), meaning the 2015 outer position does not match the standard back up light position for that same year.
The 2010 outer back up light has a mid-year specification change. Units produced up to March 2010 use the 7440, while those produced from March 2010 onward use the 3057, making production date a necessary reference point for that model year.
The 921 and 7440 are both single-filament wedge bulbs sharing the same 12V operating voltage, but they differ in wattage and base size (T15 versus T20), which means they are not interchangeable despite their similar form factor.
The 3057 carries a dual-filament design, distinguishing it from both the 921 and 7440. Its presence in the 2010 outer back up light position on later-production units reflects a different circuit requirement than the single-filament types used elsewhere in the xB lineup.
The 2009 outer back up light specification includes a "Lower" qualifier for the 7440 fitment, indicating a positional distinction within the outer light assembly for that model year.