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My ebike has been acting weird lately, and I need help figuring out why. It's my daily driver, so I'm hesitant to turn it in for service, as that would probably take at least a month. The bike's one of these. It's built to follow Norwegian/European requirements, which means it has a pedal-assist sensor and a max speed of 25 km/h. It also has e-brakes, meaning the motor is disengaged at the slightest use of the brake handles. Settings are pretty limited with three assistance settings (low, mid, high), in addition to a walk-assist button and the on/off switch. It's mostly stored indoors, both at home and at work. It's only left outside for shorter periods of time when I'm visiting friends and family.

Some observations:

  • The motor sometimes does not work at all, and only provides assistance in short, inconsistent bursts, completely disregarding set assistance level.
  • The motor will be always on, disregarding the pedal-assist requirement, just blasting full throttle unless I squeeze the brakes.
  • The on/off button seems to work fine. As in, when the bike has the battery connected but is switched off, the motor does not engage.
  • Most of the time, the bike works perfectly.
  • Possibly coincidental, but the incidents have always happened on/after rainy days.
  • I first experienced this after leaving the bike unused while on vacation for 3 weeks.
  • All incidents have occurred on a fully or near fully charged battery.

Hypotheses:

  • This is somehow related to a wet battery-connection.
  • Pedal-assist sensor is broken.
  • Ebrakes are not working properly.

The battery and connector both look fine. I have not yet inspected the wiring or the motor itself. I am grateful for any assistance with how to proceed. Thanks!

  • If Ivan's suggestions don't work then a shop service might be in order. You could try expediting the repair - a month is ludicrous! A day should be more than enough for planned work, and ask if they have loan bikes for the time. – Criggie Aug 8 '17 at 22:21
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The unusual bursts / full blast behavior could be related to your cadence sensor at the bottom bracket. Depending on the type, it could be related to water ingress / corrosion to the sensing contacts, causing false pedaling to be registered. Also makes sense if it happens around rainy days as water might affect the sensing.

Do you have a throttle you can use to isolate the problem?

  • Thanks, I'll check the sensor. Anything specific I should look for? I don't even know how they work. Could it being dirty be enough to throw it out of whack (quite alarming if that's the case, really)? I have the walk-assist button, which could be used to check if the motor runs without pedalling, but it only works up to 6 km/h. Otherwise no throttle, I'm afraid. – Plasma Aug 8 '17 at 7:39
  • Unfortunately throttles don't exist on newer models (having ridden one I much prefer a throttle to pedal assist). A busted switch is likely to be the issue though. "Cadence sensor" might be putting it a little strongly but some sort of switch in the crank area is probably the problem. This could easily explain the "nothing at all" situation as well. – Chris H Aug 8 '17 at 10:00
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    +1 it's the pedal sensor. Usually these aren't something you'd fix but instead you'd just swap it out. First make sure all the magnets in the crank are there and the. If they are, swap out the cadence sensor. You might also check the connector for corrosion and put anticorrosion grease on it. – RoboKaren Aug 8 '17 at 16:35
  • I'll keep an eye on the sensor. I checked it yesterday and apart from being a bit dirty, there's nothing obviously (to me, anyway) wrong with it. I cleaned it off and it worked fine today. I'll get a chance to test in the rain this afternoon. If it's acting up again, I guess I'll turn it in for service. It's only four or five months old, I hoped it would last longer. But maybe that's what you get for going with the cheapest alternative. – Plasma Aug 9 '17 at 6:31
  • Indeed it's hard to say or see depending the type of sensor on there. I'd go with what @RoboKaren suggested. Good luck on getting to the bottom of it. – IKY.LI Aug 9 '17 at 11:35

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