The engine control module controls nine vanes for the turbocharger. The vanes are used to vary the amount of boost pressure and can control the boost pressure independent of engine speed. The vanes mount to a unison ring which are rotated to change the vane angle. The engine computer will vary the vane angle which adjusts the boost depending upon the load that applied when you accelerate the pedal at the require speed of the engine.
The turbocharger vanes are normally open when the engine is not under load. However, the engine main computer will often close the turbocharger vanes to create back pressure to drive exhaust gas through the exhaust gas re circulation recognized as the egr or egr delete valve. Does at extreme cold temperatures, the engine computer may close the vanes at low load conditions in order to accelerate engine coolant heating .temperature and when reach the optimum performance temp the turbo vanes will open as require from the engine computer. The engine computer may also close the turbocharger vanes under exhaust braking conditions, only when is below the command coolant temperature
During engine diesel regeneration, the engine will vary the turbocharger vanes to assist with the exhaust system warm-up, and to maintain proper engine exhaust temperatures needed to properly regenerate the exhaust particulate filter called the dpf or dpf delete.