Intermittent Power Loss While Riding an E-Bike

Intermittent power loss while riding is probably the most difficult problem to diagnose on an ebike as it can be caused by many different things. The parts that could be causing this are:

  • Controller
  • Battery
  • Motor
  • Wiring Harness
  • Pedal Assist Sensor
  • Throttle
  • Brake Kill Switches

So as you can see, this is a big list and includes most of the electrical components on the bike. To properly diagnose the power loss, we have to first look a little deeper in what is happening when the power loss occurs.

Does the whole bike shut down randomly?

Or is it just power loss in the throttle or pedal assist?

The answer to this question will dictate which way we go in the diagnosis. If it is powering off completely, then it is more than likely a battery or connection issue somewhere. If there is intermittent power loss to the throttle or pedal assist, it is more than likely an issue with the motor or controller.

Power Loss Where Bike Shuts Down

If you are having power loss where the whole bike shuts off randomly while riding, it is more than likely a battery or connectivity issue. The likely culprit is the battery most of the time, but it can be a loose connection elsewhere on the bike. The first thing you should do to check this is go through the bike and inspect all of the connections. There may be a plug that has come a little loose and may not be making a constant connection, which could lead to power loss. Here is a video walking through the process of checking the connections:

Check over all of the connection ports and make sure they are all firmly in place. It may be helpful to unplug and replug them in just to be safe. After all of the connection ports have been checked, try to see if it solves the problem.

If this does not resolve the issue, the next step is to check the battery connections. Looking at the battery connections, you should see the silver contact points in the battery slots.

Electric Bike Battery Connection Terminal

The picture to the right  shows what the contact points on the battery should look like. You should be able to see almost the whole silver contact point. If you do not see them, or they appear to be hidden underneath the black shell, then this may be causing the intermittent power loss. If those contact points get stretched out and are not in their proper position, sometimes when you hit a bump while riding, they could lose contact with the controller, which would cause a momentary loss of power to the ebike. To remedy this issue, new connection points must be installed. To install new connection ports, please see the Battery Services Guide.

If the connections were not the issue and appear to be fine, the next step would be to replace the controller.

Power Loss Where the Bike Loses Motor Power, But Stays On

If you are having power loss on your ebike while using it, but the bike itself stays on, the causes are a bit different than in the previous section. Where the last section was focused on battery/power related parts, this form of power loss focuses on the parts that actually propel the bike or actuate the power. This would include the pedal assist sensor, the throttle, the motor, the wiring harness, and of course, the controller. The issues with the bike losing power but staying on is more than likely due to some part that communicates with the motor not functioning properly. The first thing to check with this issue would be to zone in on what is happening when the power loss occurs. You should also run through the No Pedal Assist and No Throttle Power sections to make sure those are not the issue. Once you have run through those sections, that would help eliminate the throttle, pedal assist sensor, and wiring harness. With those parts eliminated from being the issue, we can focus on the remaining parts: the motor and the controller. The first thing that we should check out is the connection between the controller and the motor. It would be a single large plug located along the chainstay of the bike. Unplug this and inspect both ends. On the motor end, make sure all of the pins appear whole, straight, and not damaged. If any of the pins are missing or damaged, this would more than likely be the cause of the power loss and a new motor would be needed.

After the pins have been inspected, you should then look at the plug end that they plug into. If any of those pin holes look damaged, then the controller would need to be replaced.

If both of the connections for the motor/controller look ok, then we move to the motor itself. This can be tough, as the motor may not be showing anything externally that would indicate it is the problem. What we need to do is see if we can make any symptoms appear. The first thing to do would be to try and throttle the ebike and see what the motor does. Occasionally if there is something wrong with the motor, we can hear sounds coming from the motor. These sounds can range from something as quiet as a brief click when the throttle is twisted, to full on grinding and whirring sounds. If any abnormal sounds occur when trying to power the motor, then the motor is more than likely the issue and should be replaced.

If no abnormal sounds occur, then we move to the final part of the troubleshooting, which would just be installing a new controller or motor and seeing if it solves the issue. The controller would usually be recommended first, as it is less expensive and easier to swap out. But if after the controller was installed and the problem did not go away, that finally leaves us with the motor to be swapped.

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