INFINITI QX4 Back Up Light Bulb Size

The INFINITI QX4 back up light uses 921, 1156, and P21W bulb sizes depending on the specific version of the vehicle. Available information covers a range of years starting in 1997 and ending in 2003.

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
2001-2003	921
1997-2000	1156

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Wedge bulb (T15). 12V, 16W.	921
ANSI standard (US & Canada). Single-filament bulb with BA15s bayonet base. 12V, 21W.	1156

Other Locations

Additional Notes

The INFINITI QX4 backup light specifications span the 1997-2003 model years, covering two distinct bulb types across that range.
The 921 bulb is a T15 wedge-base type rated at 12V and 16W. The T15 designation refers to a tubular bulb roughly 15/8 inches in length, and the wedge base means the glass envelope itself acts as the retaining mechanism with no separate metal base.
The 1156 bulb uses a BA15s bayonet base with a single filament, rated at 12V and 21W. The BA15s designation indicates a single-contact bayonet fitting with a 15mm base width.
Both bulb types conform to ANSI standards applicable in the United States and Canada.
The INFINITI QX4 uses the 921 bulb for the 2001-2003 model years and the 1156 bulb for the 1997-2000 model years.
The two bulb types are not interchangeable. The 921 uses a wedge base while the 1156 uses a bayonet base, making the socket designs physically incompatible between the two production periods.
The wattage also differs between the two types. The 1156 draws 21W compared to the 921's 16W, meaning the two bulbs produce different light output levels and place different electrical loads on the circuit.
The change in bulb type between the 2000 and 2001 model years represents a shift in both the base configuration and the wattage specification for the QX4's backup light circuit.