The automatic transmission in your vehicle transmits power from the engine, through the drivetrain, and to the wheels. Inside the transmission is a system of gears and other moving components that are lubricated and cooled by hydraulic oil called ATF (Automatic Transmission Fluid). The ATF is also used to control some of the functions of the transmission through hydraulic pressure.
The transmission oil filter keeps the ATF free from contamination. It keeps damaging dirt and debris from causing damage to the gears and other components of your transmission. The filter itself may be made up of a paper element or a metal screen mesh. In either case, ATF is forced through the filter whenever the transmission is in operation. As the ATF passes through the filter, contaminants are trapped.