Controlling Turbocharger (TC) Boost Pressure
WARNING: This page is about a different car, the 2002 Volvo C70, 2001 Volvo C70, 2000 Volvo C70, 1999 Volvo C70, and 1998 Volvo C70. However, it is still accessible from the selected car via links, so may be relevant.
When the engine control module (ECM) determines that a higher boost pressure is permissible, the turbocharger (TC) control valve opens further and a proportion of the pressure acting on the boost pressure control (BPC) valve pressure servo is allowed through to the turbocharger (TC) inlet. In this way the control pressure is reduced, the boost pressure control (BPC) valve opens later and turbocharger (TC) pressure can increase.
The engine control module (ECM) affects the turbocharger (TC) control valve by grounding one of the terminals with a fixed frequency where the signals duty cycle determines how much the valve should open and therefore how much the boost pressure can increase.