Valve Body (Automatic Transmission)

It is a metal block with many fine channels, valves and springs, mounted under or inside the gearbox and bathed in transmission fluid. In modern automatics, electric solenoids on the valve body are controlled by the transmission control unit; older units relied more on purely hydraulic logic. Some manufacturers sell the valve body together with the control unit as a single mechatronic unit.

Pressurised fluid from the transmission pump passes through the valve body, and the valves and solenoids direct it to the clutches and brakes needed for each gear.

Worn bores, sticking valves or contaminated fluid cause harsh or delayed shifts, slipping and gear-ratio fault codes. Using the correct fluid and changing it as recommended helps keep the narrow passages clean.