Fiat 500X Back Up Light Bulb Size

The Fiat 500X back up light requires a P21W bulb size for proper installation and function. Available data covers the range from 2016 through 2023 for the specified vehicle component.

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
2016-2023	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 Fiat 500X uses the P21W bulb for its back up light across the 2016-2023 model years.
The P21W is an ECE-standardized bulb type, meaning it conforms to European and internationally recognized automotive lighting regulations rather than SAE standards used in North American specifications.
P21W bulbs operate at 12 volts and consume 21 watts, which is a typical power rating for single-filament signalling applications such as reverse lights.
The P21W uses a BA15s bayonet base, a single-contact fitting where the "s" denotes a single pin offset, distinguishing it from the dual-contact BA15d variant with which it is not interchangeable.
As a single-filament bulb, the P21W serves one dedicated lighting function, unlike dual-filament types that combine two functions such as braking and running light in one unit.
The BA15s bayonet base requires a quarter-turn insertion method, as opposed to a wedge-base bulb, which is pressed directly into its socket without rotation.