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The ECU transmission control unit is an on-board computer which electronically controls the transmission of the vehicle. TCUs can be separate from, or in this case, attached to the ECU. The ECU Transmission Control unit contacts sensors that are placed around the vehicle to receive data in order to accurately calculate when to change gears and which gear to use as well as improve fuel economy and drive quality.
These sensors include the vehicle speed sensor, the wheel speed sensor, the throttle position sensor, the turbine speed sensor and the transmission fluid sensor. The TCU also uses data sent from the ECU. This controls and maintains the efficient running of the engine as well as scanning for any abnormalities in its function.
If a ECU transmission control unit begins to fail, you may notice a loss of power, error message or difficulty in changing gears. This problem can be intermittent at first, and can sometimes be rectified temporarily by turning off your car and turning it back on again after a short while. Ultimately though, any damage to a ECU transmission control unit will need to be repaired to correct the fault.