GMC Envoy Back Up Light Bulb Size

Additional Notes

• The GMC Envoy uses the 3157 bulb size for its back up light across the 2002-2009 model years.
• The 3157 is an ANSI-standardized bulb type, meaning its specifications are governed by a recognized North American standard applicable in both the United States and Canada.
• The 3157 is a dual-filament bulb, meaning it contains two separate filaments within a single housing, each operating at a different wattage.
• The two filaments in the 3157 operate at 27W and 7W respectively, with the higher-wattage filament typically serving the primary function and the lower-wattage filament serving a secondary role.
• The 3157 follows the T25 wedge form factor, which refers to a wedge-base construction that seats directly into a compatible socket without a separate metal base or pins.
• The bulb operates on a 12V electrical system, consistent with the standard automotive voltage found in passenger vehicles and light trucks.
• Because the 3157 is a dual-filament type, substituting it with a single-filament equivalent such as the 3156 would result in the loss of one lighting function and is not a direct replacement.
• The consistent use of the 3157 across all eight model years of the Envoy covered in these specifications means a single bulb part number applies to the full production range represented here.