Because the automatic transmission is linked to the engine by a fluid coupling, rather than by the mechanical clutch of a manual transmission, there is a potential loss of efficiency due to slippage. The lockup torque converter improves fuel economy by eliminating this slippage. An internal clutch system provides a positive, direct connection between the engine and transmission. It is usually controlled by the power train computer and will operate only after the vehicle has moved away from a stop or shifted out of low gear.