The controller of an electric vehicle is called its brain: it commands the motor to start, run, go forward and back, accelerate, decelerate, and stop. If the controller goes wrong, the electric vehicle is paralyzed.

When you find that an electric vehicle rides noisily, slows down under load, cannot start from a standstill after stopping, and only rides normally once the motor is already turning, what fault is this?

The preliminary diagnosis is motor phase loss, because modern controllers are intelligent, and under phase loss a start from a standstill will shudder.

Phase loss has two possibilities. One is a fault caused by damaged Hall sensors in the motor; the other is a problem in one of the phase-line circuits inside the controller. We should first carefully check the connecting wires and the Hall sensors. If every test comes back normal, then a component inside the controller has failed, and the only solution is to replace the controller!

While riding, road conditions are complex: potholes, uphills and downhills, accelerating and decelerating, all of which shake the controller. So when replacing a controller, be sure to mount it firmly and tighten it with anti-slip screws, so that bumps on rough roads cannot loosen the solder joints of the controller components and cause shorts and damage!

Sometimes we find that an electric vehicle gets power but will not move, pushing it feels heavy, and it makes a jerking clunk-clunk sound while pushed. This happens when a loose motor wire causes a short circuit. You can unplug the three thick phase wires of the motor: if the pushing effort disappears, the controller is broken and needs replacement.

The second possibility is the motor itself: shorted and burnt motor coils also produce this kind of symptom.

The electric-vehicle observer notes that when the vehicle has power but will not move and the wheels cannot turn, it is usually an internal controller fault. Never force-push while the wheels are locked; first unplug the three thick phase wires. If the vehicle then rolls freely, the controller is fine and the motor is the one that needs repair!

The controller has many functions and a lot of wiring. Sometimes installers, being lazy and looking for shortcuts, figure that if the motor turns, it is fine, and leave function wires unconnected. Wires for functions such as automatic repair, brake power cut-off, cruise control, three-gear speed change, and reverse must all be connected too, not only for convenience but also for better after-sales guarantee service.