Cadillac STS high beam headlight bulbs use 9005 size, while low beam headlight bulbs use H11 or D1S size specifications. The replacement chart covers 2005 through 2011 model years with corresponding bulb size data.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 9005 bulb is an ANSI-standard single-filament halogen type rated at 12V and 65W, fitted with a P20d base. It serves as the high beam headlight bulb across all specified model years of the Cadillac STS, covering 2005, 2010, and 2011.
The H11 is an ECE-standard single-filament halogen bulb rated at 12V and 55W, using a PGJ19-2 base. Although it originates from European and worldwide standards, it carries US approval as well. It functions as the low beam bulb on STS vehicles equipped with halogen capsule headlamps across the 2005-2011 specified years.
The D1S is an ECE-standard high-intensity discharge bulb operating at 85V and 35W, fitted with a PK32d-2 base. Unlike the halogen options, it incorporates an integral ignitor and is designed specifically for projector-type housings. It serves as the low beam bulb on STS vehicles equipped with HID headlamps across the same specified years.
The Cadillac STS low beam position accommodates two distinct and incompatible bulb types depending on the headlamp system installed. The H11 and D1S are not interchangeable, as they differ in operating voltage, base type, and housing requirements.
The 9005 and H11 both operate on a standard 12V automotive electrical system, while the D1S requires 85V, supplied through a dedicated ballast unit that is part of the HID headlamp assembly.
The P20d base of the 9005 and the PGJ19-2 base of the H11 are physically distinct, preventing cross-installation between the high beam and low beam halogen positions despite both bulbs being single-filament halogen types.
The D1S integral ignitor is a built-in component that initiates the high-voltage arc required to strike the xenon discharge. This design differs from older HID systems where the ignitor was a separate external component.
The 9005 follows ANSI standards primarily used in North America, while both the H11 and D1S follow ECE standards. The presence of all three bulb types across the STS specifications reflects the use of both regional standardization frameworks within a single vehicle platform.