There is a TSB 01-07-09 for your vehicle covering the G68 speed sensor. A faulty connector wiring is apparently the problem.
Go [http://workshop-manuals.com/volkswagen/jetta/v6-2.8l_(afp)/sensors_and_switches/sensors_and_switches_transmission_and_drivetrain/sensors_and_switches_a/t/transmission_speed_sensor_a/t/component_information/technical_service_bulletins/all_technical_service_bulletins_for_transmission_speed_sensor/0107-09/jan/07/a/t_controls_mil_on/dtc_00281_in_tcm_memory/|here] and you can read about it yourself it also instructs you how to fix it. But at least it will give you some good information.