For the 2003 Cadillac CTS, the high-beam headlight uses a 9005XS bulb. Low-beam fitment depends on the headlight type: models with halogen headlights use 9006XS, while models with HID headlights use D1S. Confirm the headlight configuration before ordering a low-beam replacement.
Other notable exterior bulbs include 3157R for the brake and tail lights, 3157 for the reverse lights, rear turn signals, and daytime running lights, and 194NA for the front side markers. Front turn-signal fitment is listed as 3157, 2825, or 98, while the license-plate, parking, and rear side-marker locations use either 2825 or 98. The center stop light uses PC175. Interior fitment includes PC175 for the dome and map lights, 564 for the courtesy light, and 211-2 for the trunk light.