1. A method for diagnosing operation in a turbocharged engine having an engine control module (ECM) operable to control engine operation in response to data received from a plurality of sensors, the method comprising: storing in a memory data corresponding to: a compressor map defining a region of compressor efficiency and compressor speeds during operation; and a turbine map defining a region of turbine efficiency and turbine speeds during operation; determining a predicted value for an operating parameter using data received from selected ones of the plurality of sensors and the at least one of the compressor map and the turbine map; determining an actual value for the operating parameter using data received from selected ones of the plurality of sensors; and generating an abnormal operation signal if a difference between actual and predicted values is greater than a predetermined amount.