Turbocharger Bypass (TCBY) Valve
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The TCBY valve(s) prevent back flow through the turbochargers when the throttle is rapidly closed to avoid undesirable noise. The high pressure downstream of the turbocharger is vented back to the intake air stream when the valve is open reducing pressure in the system.
Two types of bypass valves are currently being used. The first is a solenoid controlled valve located in a crossover tube between the turbocharger intake side and the pressurized output to the charge air cooler (CAC). The second type of bypass valve is an electropneumatically controlled system consisting of a vacuum source, control solenoid, tubing and a vacuum controlled bypass valve that is integrated into the turbocharger housing.