The transmission in a Volkswagen Jetta contains a large number of electronic components. These components are controlled by a stand-alone computer called the transmission control unit, or TCU. When the TCU senses a problem with the transmission, it stores a diagnostic trouble code, or DTC, in its memory. It also illuminates the “Service Vehicle” light on the dashboard. Clearing the DTC from the TCU’s memory resets the transmission and turns off the “Service Vehicle” light on the dashboard.
Shift the Jetta’s transmission into park or first gear (on a manual) and turn off the engine. Turn the ignition switch to the “ON” position.
Connect the data cable of an automotive scan tool to the Jetta’s 16-pin diagnostic data port, located underneath the dashboard on the driver’s side of the vehicle. Power on the scan tool.