GMC Envoy XL Back Up Light Bulb Size

The GMC Envoy XL back up light bulb size is 3157, a specific bulb designation for this vehicle model. The replacement chart covers 2002 through 2006 production years with corresponding bulb size specifications.

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
2002-2006	3157

Bulb Specifications

Description	Bulb Size
ANSI standard (US & Canada). Dual-filament wedge bulb (T25). 12V, 27W/7W.	3157

Other Locations

Additional Notes

The GMC Envoy XL uses the 3157 bulb for the back up light across all listed model years, spanning 2002-2006.
The 3157 is classified under the ANSI standard, meaning it conforms to a standardized specification recognized in both the United States and Canada.
This bulb follows the T25 wedge form factor, which refers to its tapered plastic base that seats directly into a matching socket without requiring a separate metal base or bayonet pins.
The 3157 operates on a 12-volt electrical system, consistent with the standard automotive voltage found in passenger vehicles.
As a dual-filament bulb, the 3157 contains two separate filaments within a single envelope, each rated at a different wattage: 27W for the brighter filament and 7W for the dimmer filament.
In back up light applications, only one of the two filaments is typically active, as the dual-filament design is more commonly associated with combination stop/tail or turn/tail functions in other positions on a vehicle.
The 3157 shares its T25 wedge base with several related bulb types in the same family, such as the 3156, 4157, and 3057, which can create substitution confusion; these variants differ in wattage ratings, filament count, or both, and are not universally interchangeable.
The 3057 is a common point of confusion with the 3157, as both are dual-filament T25 wedge bulbs at 12V, but the 3057 is rated at 27W/8W rather than 27W/7W, reflecting a slight difference in the low-filament output.
The 3156 is a single-filament variant in the same family and is not a direct replacement for the 3157 in sockets wired to use both filaments, as installing it in such a socket would result in loss of one lighting function.