BMW X4 Daytime Running Light Bulb Size

The BMW X4 daytime running light requires bulb size H7 or P21W depending on the specific version of the vehicle. Data for the lighting components covers the period from 2017 to 2021.

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
2021	H7
2017-2018	P21W

Bulb Specifications

Description	Bulb Size
ECE standard (Europe & worldwide). Single-filament halogen bulb with PX26d base. Also approved in the US and Japan. 12V, 55W.	H7
ECE standard (Europe & worldwide). Single-filament signalling bulb with BA15s bayonet base. 12V, 21W.	P21W

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Additional Notes

The BMW X4 daytime running light specifications reference two bulb types: the H7 and the P21W, both governed by ECE standards recognized across Europe and worldwide markets, with the H7 also carrying approval in the United States and Japan.
The H7 is a single-filament halogen bulb rated at 12V and 55W, fitted with a PX26d base, a two-pin connector that locks into a dedicated socket and is not interchangeable with bayonet-style fittings.
The P21W is a single-filament signalling bulb rated at 12V and 21W, using a BA15s bayonet base, which is a single-contact bayonet cap with offset pins to ensure correct orientation during installation.
The wattage difference between the two types is substantial: the H7 draws 55W while the P21W draws 21W, reflecting their distinct electrical and thermal requirements and confirming that the two types are not substitutable for one another.
The BMW X4 (2021) uses the H7 bulb for the daytime running light position, while the 2017-2018 model years use the P21W in that same position, indicating a change in bulb specification between those production periods.
Because the H7 uses a PX26d base and the P21W uses a BA15s bayonet base, the two bulbs require physically different sockets, making cross-year fitment incompatible without modification to the housing.