Chevrolet Silverado Back Up Light Bulb Size

Additional Notes

• The 921 bulb is the most frequently specified backup light bulb across the Chevrolet Silverado lineup, appearing in the majority of model years from 1999 through 2024 and covering a wide range of trim and cab configurations.
• The 921 is a T15 wedge-base bulb rated at 12V and 16W. Its wedge base design means it is held in place by the socket itself rather than by a locking mechanism, which distinguishes it from bayonet-style bulbs.
• The 1156 bulb uses a BA15s single-contact bayonet base, a physically distinct mounting style that is not interchangeable with wedge-base sockets. It is rated at 12V and 21W, making it slightly higher in wattage than the 921.
• The 2024 Silverado uses the 1156, while the 2022-2023 models use the 921, meaning the base type changed between the 2023 and 2024 model years. These two bulbs are not interchangeable due to their different base designs.
• The 2021 Silverado has three separate backup light bulb specifications depending on the sub-model and bed configuration. The 1500 and 3500 without the Fleetside bed take the 1156, the 1500 and 3500 with the Fleetside bed take the 921, and the 2500 HD takes the 921.
• The 3047 and 3156 are both single-filament T25 wedge bulbs rated at 12V and 27W. Because they share the same base type, wattage, and voltage, they are generally considered interchangeable in practice.
• The 3157 is a dual-filament T25 wedge bulb rated at 12V with a 27W high filament and a 7W low filament. Although it shares the T25 wedge base with the 3047 and 3156, its dual-filament construction means it is not a direct drop-in replacement for single-filament T25 bulbs in all socket configurations.
• The 2005-2006 Silverado HD models (2500/3500) transitioned from the 3157 to the 3047 by the 2007 model year, shifting from a dual-filament to a single-filament T25 bulb for the backup light position.
• The 2000 Silverado is the only model year in the specifications where the 1500 and 2500 HD sub-models are reversed in their bulb assignments relative to later years, with the 1500 using the higher-wattage 3156 and the 2500 HD using the lower-wattage 921.
• All four bulb types listed across these specifications (921, 1156, 3047, 3156, and 3157) conform to ANSI standards applicable in both the United States and Canada, indicating standardized electrical and physical ratings across the range.