Line Pressure Control Valve
WARNING: This page is about a different car, the 2006 Suzuki Verona. However, it is still accessible from the selected car via links, so may be relevant.
The line pressure control valve sets the general pressure level in the valve body. When gearshifts are not taking place, the line pressure varies between 2 levels, depending on the turbine torque. Line pressure increase linearly by time. But it has a limit point. When pressure reaches that point, excess oil pressure drains back into the oil sump.