Electrical Components - Design And Function: Transmission: Overview
AW55-51 is a 5 speed electronically controlled automatic transmission with a lock-up function for the three highest gears. The transmission control module (TCM) adapts the gear changes to ensure that the correct gear is selected for the driving mode, engine load, driver requirements, speed etc. This gives good fuel economy combined with increased comfort by ensuring smoother gear changes and lower noise levels.
In a vehicle with an automatic transmission, the driver neither needs to decide which gear should be used nor shift gear. There is a operating system in the AW55-51 which uses a torque converter and gear shift system to do this.