The diagram shows the boost pressure system for a turbocharger with variable turbine geometry and solenoid valve control
1 Boost pressure control solenoid valve
2 MAP sensor
3 IAT sensor
4 Intercooler (not on all versions)
5 Vacuum unit for variable turbine geometry
6 Turbocharger(s)
7 PCM
8 Vacuum pump
The figure depicts the charge air system of a turbocharger having variable turbine geometry and electrical turbocharger guide vane adjustment actuator
1 T-MAP sensor
2 Intercooler (not on all versions)
3 Electrical turbocharger guide vane adjustment actuator
4 Turbocharger(s)
5 PCM
On a variable geometry turbocharger, the boost pressure is regulated by adjusting the guide vanes. The optimum boost pressure can therefore be set for every operating condition.
The boost pressure actual value is measured via the MAP sensor. The required value is dependent on the engine speed and the injected fuel quantity as well as the IAT and BARO correction factors.
In the event of a discrepancy, the guide vanes of the variable geometry turbocharger are re-adjusted via the boost pressure control solenoid valve or the electrical turbocharger guide vane adjustment actuator.
In the event of a malfunction of the boost pressure control system, engine power is reduced via the fuel metering system.
With wastegate turbochargers (not shown here), the MAP signal is used as a safety function if the wastegate does not open after a specified boost pressure has been reached. The engine power is also reduced in this case.