Chevrolet Astro Back Up Light Bulb Size

The Chevrolet Astro back up light utilizes 1156 and P21W bulb sizes for various applications across the production history. Available data covers the range from 1985 to 2005.

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
1985-2005	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 Chevrolet Astro uses the 1156 bulb for its back up light across all model years from 1985 to 2005, representing an uninterrupted 21-year span of consistent fitment for this position.
The 1156 is a single-filament bulb, which is the standard construction for back up lights, as this application requires only one lighting function rather than a combined stop/tail arrangement.
The 1156 operates at 12 volts and 21 watts, placing it within the typical power range for incandescent automotive signal and reverse lighting.
The bulb uses a BA15s bayonet base, where "BA15s" denotes a single-contact bayonet fitting with a 15mm base width, distinguishing it from the dual-contact BA15d base found on two-filament bulbs.
The 1156 carries ANSI standardization recognized in both the United States and Canada, meaning the designation refers to a consistent specification rather than a proprietary or manufacturer-specific part number.
The BA15s single-contact base of the 1156 is not interchangeable with the physically similar 1157 bulb, which uses a BA15d dual-contact base and would not seat correctly in a socket designed for the 1156.