My Purion is not working properly

[Yoak]

Yesterday I broke my gx derailleur. Bought an new one and fitted it. When I tried my bike I noticed the motor was turning on and off and I was only doing 20km/h (Garmin)
Looked at the Purion display and the speed was reading all over the place. Jumping from 14 to 28 km/h
Bike is 2 weeks old, and no hacking or trimming of any kind involved
Anyone got any ideas?

 

[Frankieboy]

Is the magnet on the rear wheel / spoke in the correct position?

 

[Yoak]

Trying the bike for the 3rd time now and it suddenly went back to normal after a few minutes. The only thing I did was going through the menu on the display and resetting the odometer.
happy it’s back to normal, but a bit worrying at the same time
I can’t see where the magnet is

 

[Frankieboy]

Do you have a gen 4 motor? I’m not sure they have one, but previous versions do.

 

[Yoak]

It’s the latest version. Not sure what gen. it is. It started acting weird again. Seems to be around 20km/h when it suddenly reads from 14-28 km completly random

 

[Frankieboy]

Early Bosch versions have a magnet on the wheel which gives an input to a sensor, so the system knows your speed. The 4th gen system (standard size chain ring) May have something different.
If you’ve only had it a few months it’s obviously covered under warranty, have you contacted your supplier? I would personally do so, for two reasons; 1) they should be able to get it sorted for you, 2) you have logged the problem with them.

 

[PhilBaker]

The Bosch gen 4 also uses a magnet on the spoke (well at least mine does), picture attached to show the alignment.

 

[Tony.OK]

The magnet is in the rear disc rotor, sensor is below rear brake caliper somewhere....make sure you haven't knocked sensor when removing wheel?

 

[Yoak]

The magnet is in the rear disc rotor, sensor is below rear brake caliper somewhere....make sure you haven't knocked sensor when removing wheel?

Nice, thanks for that info. I’ll check after work today

 

[Yoak]

Found the magnet connected on the inside of the disk break. Took off the wheel and cleaned everything. Didn’t look dirty and it can’t really go out of alignment it looks like. It was acting funny before I did this, but it seemed to behave correctly again after I put the wheel back. I hope it will stay ok this time. I got the bike directly from the importer so it’s not as easy as dropping by my LBS this time around

 

[Yoak]

Took my bike for a little spin. It was working ok until I had a transport section on kind of flat gravel road. It started cutting off abruptly when I was doing 20, and I saw the display jumping up to 28 then down to below 20 and up and down. When I hit the technical trails I didn’t have any issues. It seems to happen under light load at around 20km/h. Guess I have to find a Bosch technician/shop

 

[Rikster]

Drop the motor there are probaly some wires beiing squashed. Had the same issue when I changed the brakes and had to drop the motor. If you ar lucky you can just reroute them and all works fine again.

Put the bike upside down while doiing this, then you have a better view where the wires have a free area to go through.

 

[Yoak]

Thanks for the input. I’ll have a look if the problem comes back. At the moment it’s working fine

 

[Yoak]

Just an update. The problem persisted, so I tried a friends wheel on my rail and the bike seemed to run properly with out the speed reading jumping all over the place.
that told me it was probably my magnet.
I took it off and cleaned it and I noticed it was lots of little metal “shavings”from the disk break on the sides of the magnet. Got rid of those and now the bike seems to work properly again.