The Volvo 940 brake light requires a P21/5W bulb size for proper installation and function. Data for the specified component covers the range from 1991 to 1993.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The Volvo 940 uses two distinct ECE-standard bulb types across its brake lighting system for the 1991-1993 model years: the P21/5W for the main brake lights and the P21W for the center high mount stop light.
The P21/5W is a dual-filament bulb rated at 12V with a 21W primary filament and a 5W secondary filament, mounted on a BAY15d bayonet base. The dual-filament design allows a single bulb to serve two functions, typically combining brake and tail light operation within one housing.
The P21W is a single-filament bulb rated at 12V, 21W, and uses a BA15s bayonet base. Its single-filament construction suits dedicated stop light applications where no secondary function is required.
The BAY15d base of the P21/5W and the BA15s base of the P21W are not interchangeable. Although both use a 15mm bayonet fitting, the BAY15d has offset pins to enforce correct dual-filament orientation, while the BA15s has a single contact and symmetrical pins.
Both bulb types conform to ECE regulations, a standard recognized across Europe and numerous markets worldwide, indicating a globally distributed specification rather than a region-specific one.
The center high mount stop light on the Volvo 940 uses the P21W across all three listed model years, reflecting the single-function nature of that lamp position, which operates only as a stop signal with no combined tail light role.
Substituting a P21W in place of a P21/5W in the main brake light position would result in the loss of the tail light function, as the P21W carries no secondary filament to fulfill that role.