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I have a Vanpowers Ultra Glide Ultra ebike which is 4 months old and has only travelled 200 km/125 miles and "Error 21" popped up on the display.

Working with Vanpowers after several questions they thought the issue is being caused by a faulty Speed Sensor and they dispatched a new one. Fitted the new sensor but problem persists. Goes for a few seconds then code appears and all power stops.

I am waiting for more advice from them. I live in Italy.

We have tried a different battery (we have 2 bikes) and unplugged and replugged the display.
No joy.

Any thoughts?

Stock image from supplier's website
Source: https://www.vanpowers.com/products/urbanglide-ultra?variant=43958176088317

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    The specs say this bike's motor is "Bafang M600 Mid Drive Motor" hopefully the errors are consistent across controllers for this motor, and not unique to that one brand of bike. Googling Bafang M600 Mid Drive Motor error 21 does indeed suggest its a problem with "improper installation and placement of the magnet in regards to the speed sensor" source intercom.help/bafangusadirect/en/articles/5071424-error-21 Check there for photos.
    – Criggie ♦
    Commented Aug 29 at 10:04

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If @Criggie is right (he usually is) then it might just be that the magnet has moved a bit out of position.
I assume your magnet is fixed to a spoke, held by a screw, either Phillips or Torx.
You should be able to see where it passes next to the speed sensor. The Bafang sensors i have worked with have a small flattish cylindrical protrusion where the actual sensor is located in the sensor housing. Try to make sure the magnet passes as close as possible to this point, and see if that fixes your problems. You do that by loosening the screw of the magnet, movie the magnet as close to the sensor as possible and tighten the screw again.
It could also be that the sensor is just too far from the spokes. You could try pushing it a bit closer, if the magnet is already as close as it can be. It's a plastic housing, so be gentle, and see if there are any bits that are adjustable, lest the housing breaks.

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    Thanks Burki. The speed sensor magnet is actually attached to the brake disc and cannot really move. I have installed a replacement sensor and magnet and still the problem exists. It maybe a faulty motor. Vanpowers are sending me a new one, so hopefully that will sort it out. Thanks again.
    – simonandjo
    Commented Sep 3 at 9:36

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