GMPartsGiant.com offers the wholesale prices for genuine 2015 Cadillac XTS parts. Parts like Horn are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 6 Cyl 3.6L. Model Code: 4 DOOR NOTCHBACK, LUXURY 4 DOOR NOTCHBACK, PLATINUM 4 DOOR NOTCHBACK, PREMIUM 4 DOOR NOTCHBACK.