Which component is not part of an automatic transmission?

The pressure plate is not a component of an automatic transmission; it is primarily associated with manual transmissions. In a manual transmission system, the pressure plate is part of the clutch assembly, which engages and disengages the engine's power from the transmission shaft, enabling the driver to shift gears.

In contrast, the other components listed are integral to the functioning of an automatic transmission. The torque converter acts as a fluid coupling between the engine and the transmission, allowing for smooth power transfer and enabling the vehicle to idle without stalling. The transmission fluid pump circulates the hydraulic fluid necessary for the operation of the automatic transmission, ensuring that all components receive the lubrication needed for optimal operation. The planetary gear set is a critical element that provides various gear ratios, allowing for automatic shifting based on the vehicle's speed and load conditions.

Understanding the specific roles of these components helps to clarify why the pressure plate does not belong in the automatic transmission's assembly.