Control valve, bypass: Notes
The pressure in the turbocharger outlet rises when the accelerator is released at the same time as the flow rapidly drops. This can cause cavitation in the pump, which means there is severe pulsation in the turbocharger's inlet and outlet. Cavitation can damage the turbocharger, cause noise and make the air mass measurement from the mass air flow sensor too high as during the pulsation, the air will move backward and forward in the inlet system.
To prevent the phenomenon described above, a bypass valve is fitted between the turbocharger outlet and inlet. The valve is opened by the vacuum from the intake manifold.
In a de-energized state, a solenoid valve will connect the bypass valve control line to the intake manifold after the throttle. During deceleration, the vacuum will open the bypass valve and connect the turbocharger outlet and inlet, preventing cavitation. During acceleration, the solenoid valve will operate and the control line will be connected before the throttle. This ensures that the bypass valve is closed securely under normal driving conditions.
The solenoid valve is powered from the main relay and is grounded from control module pin 51.