what controls vgt duty cycle
An audible VGT test can be performed using a diagnostic system (AutoEnginuity, for example) to control the VGT system. With the diagnostic system active, run the engine and command the VGT to the closed position, or an 85% duty cycle. The turbocharger should make a hissing or whistling noise. Next, command the VGT to the open position, or a 15% duty cycle. Noise from the turbine side of the turbocharger should subside.