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A transmission control unit or TCU is a device that controls modern by Text-Enhance" href="http://en.wikipedia.org/wiki/Transmission_control_unit">electronic automatic transmissions. A TCU generally uses sensors from the vehicle as well as data provided by the Engine Control Unit to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality.

Electronic automatic transmissions have been shifting from purely hydromechanical controls to electronic controls since the late 1980’s. Since then, development has been iterative and today designs exist from several stages of electronic automatic transmission control development. Transmission solenoids are a key component to these control units.

The evolution of the modern automatic transmission and the integration of electronic controls have allowed by Text-Enhance" href="http://en.wikipedia.org/wiki/Transmission_control_unit">great progress in recent years. The modern automatic transmission is now able to achieve better fuel economy, reduced engine emissions, greater shift system reliability, improved shift feel, improved shift speed and improved vehicle handling. The immense range of programmability offered by a TCU allows the modern automatic transmission to be used with appropriate transmission characteristics for each application.

On some applications, the TCU and the ECU are combined into one unit, a Powertrain Control Module or PCM

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