Subaru Outback Back Up Light Bulb Size

Additional Notes

• The Subaru Outback backup light specifications cover model years 2008-2024 and reference two distinct bulb types: the 921 and the 1157, both of which conform to ANSI standards recognized in the United States and Canada.
• The 921 is a T15 wedge-base bulb operating at 12 volts with a 16-watt output. Its wedge base means it is held in place by tension from the socket itself rather than by a locking bayonet mechanism.
• The 1157 is a dual-filament bulb with a BAY15d bayonet base, rated at 12 volts and carrying two wattage ratings of 21W and 5W corresponding to its two filaments. The BAY15d base features two pins offset at different heights to prevent incorrect insertion.
• The Subaru Outback (2008-2021) uses the 921 bulb for the backup light position, making it the more widely specified of the two types across the model's history covered in these specifications.
• A bulb change occurs with the 2022-2024 Outback, which uses the 1157 instead of the 921. These two bulbs are not interchangeable due to their different base types, wattage ratings, and filament configurations.
• The 1157's dual-filament design is a notable distinction from the single-filament 921. In a backup light application, only one filament is typically active, though the socket and wiring must still be compatible with the 1157's BAY15d base.
• The 921 and 1157 share the same 12-volt operating voltage, but their base types and wattage ratings differ enough that substituting one for the other is not supported by these specifications.