Geo Storm Back Up Light Bulb Size

The Geo Storm back up light requires bulb sizes 1156 and P21W according to the provided specifications for the lighting components. Data for the bulbs covers the range from 1990 to 1993.

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
1990-1993	1156

Bulb Specifications

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

Other Locations

Additional Notes

The Geo Storm uses the 1156 bulb for the back up light across all listed model years, spanning 1990-1993.
The 1156 is a single-filament bulb, meaning it serves one lighting function rather than combining two, such as stop and tail, into a single unit.
It operates on a 12-volt electrical system at 21 watts, which is consistent with standard automotive low-voltage DC power.
The 1156 uses a BA15s bayonet base, a single-contact mount where the bulb locks into the socket with a twist rather than a threaded or push-pin connection.
The 1156 designation follows ANSI standards, indicating the bulb conforms to specifications recognized across the United States and Canada.
Because the 1156 is a single-filament type, it is not interchangeable with the visually similar 1157, which carries a dual-filament design and a different pin configuration despite sharing the same bayonet base style.