GMPartsGiant.com offers the wholesale prices for genuine 2019 Cadillac ATS Coupe parts. Parts like Automatic Transmission Case Extension 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: 2 DOOR COUPE, 2 DOOR LUXURY COUPE, 2 DOOR PERFORMANCE COUPE, 3 DOOR PREMIUM COUPE.