Boost Valve
WARNING: This page is about a different car, the 2003 Dodge Dakota. However, it is still accessible from the selected car via links, so may be relevant.
The boost valve (Fig 1) provides increased fluid apply pressure to the overdrive clutch during 3-4 upshifts (Fig 2), and when accelerating in fourth gear. The boost valve also serves to increase line pressure during torque converter lock-up.
Courtesy of DAIMLERCHRYSLER CORP.
Courtesy of DAIMLERCHRYSLER CORP.