Boost pressure actuator/boost pressure control

A turbocharger with variable turbine geometry and without a ”wastegate” is used for turbo pressure control. On the exhaust side there are adjustable blades on the outside of the turbine on rotating bearings. Those blades vary the force applied to the turbine by the exhaust, thereby altering, as required, the charge pressure generated by the turbocharger.


- Turbocharger with variable turbine geometry
- Vacuum unit with control rod
- Pressure converter, vacuum hoses


The adjustable blades are adjusted by a control lever on the turbine housing. The control lever is linked to the vacuum unit on the turbocharger by a control rod. The vacuum unit moves the control rod in and out according to the vacuum applied to it.

The pressure converter connects the vacuum unit with the vacuum supply by means of hoses. Depending on the activation status and controlled by the DDE control unit, it switches a variable vacuum to the vacuum unit. In this way, the control rod is set in the required position. The pressure converter is activated by a square-wave signal with duty factors (= variable pulse width) between 5% and 95%.

Checking variable turbine geometry

- Maximum stroke of control rod: 10 mm
- the control rod must be fully RETRACTED (= maximum turbo pressure) at 650 mbar vacuum applied at the vacuum unit
- the control rod must be fully EXTENDED (= minimum turbo pressure) at 0 mbar vacuum applied at the vacuum unit


The following turbocharger pressure control faults are detected by the DDE control unit:

  • 4180, 4191, 41A2, Turbocharger pressure adjuster activation
  • 41A3, Excess temperature output stage
  • 4521, Turbocharger pressure control negative discrepancy, turbocharger pressure too high
  • 4530, Turbocharger pressure control positive discrepancy, turbocharger pressure too low
  • 3F25, dynamic monitoring of charge air hose, charge air hose dropped (on M47TÜ as of software V43)
  • 3F35, monitoring of charge air hose idling, charge air hose dropped (on M47TÜ as of software V43)


- Turbo pressure control is deactivated
- Exhaust gas recirculation is deactivated
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