An emissions retrofit system for diesel passenger locomotives, including a single catalyst system that cleans the exhaust of both the large main engine which provides propulsion power and the smaller diesel engine which provides hotel power to supply heating and air conditioning of the passenger rail car cabines. The system includes a bolt on diesel exhaust fluid tank, a special exhaust heater inline with the small engine exhaust system and a single deisel exhaust fluid injection point in the small engine exhaust duct that provides the ammonia reductant for both engines exhaust gases