For the 2019 Cadillac ATS, the headlight bulb size depends on whether the vehicle has halogen or HID headlights. Confirm the headlight type before ordering, since the two systems use different bulbs.
- Halogen headlights: 9012 bulbs are used for both the low-beam and high-beam functions.
- HID headlights: D3S bulbs are used for both the low-beam and high-beam functions.
This means the low beam and high beam share the same bulb type within each headlight configuration, but a halogen-equipped ATS does not use the same bulb as an HID-equipped model. Check the existing headlamp assembly or vehicle equipment information to identify the correct configuration before purchasing replacement bulbs. The supplied fitment data does not list a fog-light, front turn-signal, or reverse-light bulb for this model year, so those applications are not included in this summary.