Turbocharger wastegate control valve (if equipped)
WARNING: This page is about a different car, the 2013 Ford F-550 Super Duty, 2013 Ford F-450 Super Duty, 2013 Ford F-350 Super Duty, and 2013 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
when the turbocharger wastegate actuator opens some exhaust bypasses the turbine and flows directly into the exhaust system limiting maximum boost and back pressure.