Bypass Valve

Bypass Valve

When the accelerator is released, the pressure at the turbo compressor's outlet rises at the same time as the flow falls rapidly. This results in the compressor pumping, causing violent pulsation to occur in the compressor's inlet and outlet due to the effect of cavitation. Pumping can result in damage to the compressor, noise and the mass air flow sensor incorrectly measuring too large a mass air flow because the pulsations move the air back and forth in the intake system.

A bypass valve is fitted between the compressor outlet and inlet to prevent the compressor from pumping. The valve is opened by vacuum from the intake manifold.









In a zero current condition, a solenoid valve connects the bypass valve's control line to the intake manifold after the throttle. When the accelerator is released, the vacuum opens the bypass valve and the compressor's inlet and outlet are connected. This prevents pumping. Depressing the accelerator activates the solenoid valve and the control line is connected before the throttle. In consequence, the bypass valve is securely closed during normal driving.

The solenoid valve is supplied with current from the main relay and grounded via pin 51 of the control module.

Diagnostics
- in the event of a break or short-circuit to ground, diagnostic trouble code P1658 will be generated.
- in the vent of a short-circuit to B+, diagnostic trouble code P1659 will be generated.
- In the event of an internal leak in the bypass valve, the current mass air flow/combustion cannot achieve the requested value.