The GMC Acadia back up light utilizes bulb sizes 921 and 12185 for the rear illumination system. Data for the specified components covers the production range from 2007 through 2019.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC Acadia back up light uses two distinct bulb types across its model years: the 921 for 2013-2019 and the 12185 for 2007-2012.
The 921 is an ANSI-standardized bulb used in both the United States and Canada, operating at 12 volts and 16 watts in a T15 wedge form factor.
The T15 wedge design means the 921 bulb connects directly through its base pins without a separate socket, a common trait in modern automotive lighting applications.
The 12185 is a Philips part number designation rather than an ANSI industry-wide standard, indicating it is a manufacturer-specific bulb intended for specialty applications at 12 volts.
Because the 921 and 12185 are different bulb types, units from the 2007-2012 model years are not directly interchangeable with those from the 2013-2019 model years without confirming socket and wattage compatibility.
The GMC Acadia (2017-2019) also carries an Inner Back Up Light position, which uses the same 921 bulb specified for the standard back up light on those same years.
The shared 921 fitment across both the standard and inner back up light positions on 2017-2019 models means a single bulb type services multiple rear lighting positions on those vehicles.