An engine pressure sensor monitoring system uses the position of a wastegate in a turbo-charged engine when known and calibrated engine operating conditions occur to provide diagnostic information for various engine pressure sensors and for the operation of the wastegate itself. Discrete measurement windows are defined for engine conditions with specific values for parameters that may include rpm, torque, injection timing and fuel consumption. Other sensor readings for intake manifold pressure, turbocharger compressor output pressure, peak cylinder pressure, and wastegate valve position during these measurement windows should match predicted values. If measured and predicted values do not match, one or more sensors may be bad and an alarm may be raised.