Please include the engine size in your next post so I can add it to the thread title. I am not sure what you mean by angle sensor, but I do know that there are solenoids and mechanical actuators that could be malfuntioning. I would first try locating the solenoids responsible for sending power to the actuators. There will probably be one for upshifting and one for downshifting. If you can determine which one controls the upshift mechanism, try manually applying power from the battery to the lead that feeds the actuator. If it doesn't shift, the actuator is likely the problem. If it does shift, then try applying power to the low current input wire that activates the solenoid. If that makes the vehicle shift the problem is between the switch and the solenoid. If it does not, then the problem is likely the solenoid. A repair manual will be helpful, if not necessary, either way, I recommend getting one.
BTW, I am moving this thread to the Honda ATV forum.
Yours truly, sincerelly, love always, Josh aka The DirtDemon.