Audi 4000 Back Up Light Bulb Size

The Audi 4000 back up light utilizes a P21W bulb size for the rear illumination system. Data for the specified component covers the period from 1980 through 1987.

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
1980-1987	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

Other Locations

Additional Notes

The Audi 4000 uses the P21W bulb for its back up light across all listed model years, spanning 1980-1987.
The P21W is an ECE-standard bulb, meaning it conforms to the Economic Commission for Europe's regulations, which govern lighting equipment used in Europe and numerous other markets worldwide.
This bulb operates on a 12-volt electrical system and draws 21 watts, which is typical for single-filament incandescent signal lighting applications.
The P21W carries a BA15s bayonet base, where "BA" denotes a bayonet cap fitting, "15" refers to the 15mm base width, and the lowercase "s" indicates a single contact at the base rather than a dual-contact configuration.
Because the P21W is a single-filament bulb, it serves one dedicated function per housing, which in this case is the reverse light circuit of the Audi 4000.
The BA15s base type is not interchangeable with the BA15d variant, as the dual-contact version carries a second contact pin offset from the first and is designed for dual-filament applications.