the present invention relates to an engine diagnostic system for detecting malfunctions in an engine system having a variable geometry turbine exhaust system . the engine diagnosis system includes an electronic control module adapted to periodically initiate a preprogrammed variable geometry turbine diagnostic routine . the diagnostic routine includes the operations of sending a sinusoidal control signal to a pressure regulator , determining the configuration of the variable geometry turbine , determining the pressure of a capsule , calculating the configuration of the variable geometry turbine as a function of the sinusoidal control signal , calculating the pressure of the capsule as a function of the sinusoidal control signal , determining if a pressure sensor is in calibration , determining if the pressure regulator is malfunctioning , determining if the variable geometry turbine position sensor is in calibration , determining if the variable geometry turbine is malfunctioning , and displaying the results of the test .