Cadillac STS Back Up Light Bulb Size

The Cadillac STS back up light uses a 3157 bulb size for this model. The replacement chart covers vehicle production years spanning 2005 to 2011.

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
2010-2011	3157
2005	3157

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

The 3157 is the sole bulb type listed across all model years of the Cadillac STS back up light specifications provided, covering 2005 and 2010-2011.
The 3157 is an ANSI-standardized bulb type, meaning its physical and electrical characteristics conform to a defined North American specification used in both the United States and Canada.
The 3157 is a dual-filament bulb, housing two separate filaments within a single unit. In automotive applications, dual-filament bulbs typically serve more than one lighting function from a single socket.
The T25 designation refers to the bulb's wedge-base form factor, which is a push-in style base that does not require a twist to lock into the socket.
The 3157 operates at 12 volts, consistent with the standard electrical system voltage found in conventional passenger vehicles.
Its two filaments are rated at 27 watts and 7 watts respectively, with the higher-wattage filament generally associated with brighter output and the lower-wattage filament used for a reduced-intensity function.
Because the 3157 is a dual-filament bulb, substituting it with a single-filament variant of similar base type would result in the loss of one lighting function at that socket position.