I am also having the same problem. Mine was cogging, thought it might be the motor and changed it, then the speedo totally reset it's self when I tried to turn it on. Took about three people about three times each to get the esc to reset (when you set the neurtral, fwd, and brake) It also seems the esc lost all it's programming. Went from a 17.5 to a 13.5 and it lost power, it would barely pizza the wheels, the 17.5 would nearly sling them off. And it still cogs after replacing the sensor wire Another racer mentioned his did the same thing and he replaced the power cap that solders on the batt terminals and it solved the problem. I have to order one, so I have yet to see if that fixes it.