To provide a diagnostic system for a turbocharged engine.

The invention relates to a method, a system, and a machine readable storage medium for diagnosing the operation of the turbocharged engine having an engine control module (ECM) capable of controlling the operation of the engine in response to data received from a plurality of sensors. During operation, the data corresponding to a compressor map defining the range of the efficiency and the speed of the compressor and a turbine map defining the range of the efficiency and the speed of the turbine are stored. Then, a predicted value over an operation parameter is determined by the use of the data received from the sensor chosen from a plurality of sensors and the data stored in a memory, and an actual value over the parameter is determined by the use of the received data. When the difference between the actual value and the predicted value is greater than a prescribed value, an abnormal operation signal is generated.