A new medium-speed, heavy-duty diesel engine and a microprocessor control system are two highlights of the 60 Series diesel-electric locomotives built by the Electro-Motive Division of General Motors. Many of the traditional control functions encountered on a locomotive are now incorporated in the microprocessor. Included among these are the monitoring and control of engine operating parameters. Engine performance is enhanced as the potential for broader and more precise control is realized. This paper describes the microprocessor control as it is applied to current production diesel-electric locomotives.