I've had that issue. For me what happened was someone previously ran the drone with a battery other than what the drone was rated for and it fused part of the chip on the mainboard which you can't really fix but to build a new board. You can check to see if 1 of the wires from that motor is shorting a connection on the board. That can be fixed by either replacing that motor or just putting a little electrical tape on the wire to cover the breach in the insulation. The only other possible cause to this is that someone soldered the ground wire of the motor into the wrong socket on the board or there's too much solder where the motor wires go on the board and soldered a short onto another component. You'll have to remove the excess solder to fix it. it should then run properly. Either way requires you to open the entire body of the drone/plane to inspect the wires & board properly. Be careful if you end up soldering to repair it cuz the board & components are susceptible to heat damage from too hot an iron....