S90 L6-2.9L VIN 96 B6304S (1998)
Valve Body: Description and Operation
A control unit is required to enable the mechanical power transmission system to operate. An hydraulic control unit is used for this purpose.
The hydraulic system consists of the following main components: hydraulic oil pump and an electronically controlled system of valves.
In the AW 30-40 transmission hydraulic control unit certain components have been replaced by electromechanical solenoid valves. In turn these solenoid
valves are controlled by the Transmission Control Module (TCM). There are no kickdown cable or governor for the same reason.
The hydraulic oil pump is a conventional gear driven pump which operates as soon as the engine is running. It is driven by the torque converter pump
hub.
The pump consists of the following parts: A split pump housing, drive gear and pump runner.
The pump draws oil from the pan through a strainer and delivers it at controlled pressure to the various transmission components. This pressure is
affected by the system pressure solenoid (STH) controlled by the TCM.
The pressure is known as the system or line pressure.
