The Cadillac ATS back up light requires a 921 bulb size for proper installation and function within the rear lighting assembly. Data provided covers the 2013 to 2019 range for the specified vehicle and component.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The 921 is the sole bulb size listed across all back up light positions for the Cadillac ATS, covering model years 2013-2019 for the standard back up light and 2017-2019 for the outer back up light.
The 921 bulb follows the ANSI standard recognized in both the United States and Canada, meaning it conforms to a standardized specification shared across North American markets.
It is a wedge-type bulb, classified under the T15 designation. The T15 designation refers to the bulb's tubular shape, with the number indicating a width of 15 eighths of an inch.
The 921 operates at 12 volts, which is consistent with the standard electrical system voltage found in conventional passenger vehicles.
The bulb carries a 16-watt power rating, placing it in the low-wattage range typical of reverse lighting applications.
The wedge base design means the bulb is held in its socket by the tension of the base itself rather than by a separate locking mechanism, which is a common fitment method for tail and reverse light assemblies.
Because the same 921 bulb size is specified for both the general back up light and the outer back up light on the ATS, both positions share identical electrical and physical fitment requirements.