GMPartsGiant.com offers the wholesale prices for genuine 2018 Cadillac ATS Sedan parts. Parts like Automatic Transmission Input Sun Gear Assembly are shipped directly from authorized GM dealers and backed by the manufacturer's warranty. Parts fit for the following vehicle options. Engine: 4 Cyl 2.0L, 6 Cyl 3.6L. Model Code: 4 DOOR LUXURY SEDAN, 4 DOOR PERFORMANCE SEDAN, 4 DOOR PREMIUM SEDAN, 4 DOOR SEDAN.