Purion display dead, won't switch on... :(


Feb 24, 2021
Carmarthen, Carmarthenshire
Hi, we've had a pair of 2021Trek Rails for coming up to a year now. Great bikes and love riding them... But we've had no end of issues with Bosch gen4 motors in them... It started off with a couple of 504 errors each, which we rode out, annoying, but easily fixed.
Then within a month or so of each other, the dreaded 500 error which resulted in a warranty Purion controller for one and motor replacements for both. Then, after a few weeks, another 500 error on one of the warranty motors. Took it to the LBS, they tried to diagnose it, cleared the codes and after consultation with Bosch apparently it was due to cold weather charging, whatever that means...the battery is charged off the bike in the living room and the bike is in the dining room.
Anyway it has worked fine again up until today, when, after being on charge all night, inserted the battery, ready to set off and the Purion won't switch on... Tried everything, new batteries in controller, battery from other bike, various battery reset options, but nothing, the purion won't switch on.... :(
Anyone else had as rotten luck..? Or any tricks to get it to switch on again...?
Its spoiling our rides now, just worrying what the next issue is going to be...


Handheld Power Tool
Jun 10, 2020
Coquitlam, BC
Seems like any electrical issue can be a show-stopper unless you have all the spare parts on hand. And it’s not like you can notice it wearing out, it just happens…and seemingly at the worst time.
This is probably why the LBS mechanics are needing additional training but more importantly the LBS’s need spare eMTB parts and that gets expensive. Waiting 3 months for a controller …no, no friggin way.


Active member
Jul 14, 2022
I had the same problem with Focus after a year and 4000km. Purion didn`t start. I got new motor. But no other problems or error codes. I`m not sure but I have a feeling that I forgot to turn the bike off before taking the battery out that time so maybe it happened because of that. In the morning when I put battery back, bike didn`t turn on…


Well-known member
Nov 1, 2018
My mate had the same problem. Didn’t use his bike for a while and then it would not switch on. Turned out Purion had died. Although a month or so out of warrenty Trek and Bosch paid for new one and the labour. i think this is quite rare so if it does happen it’s pretty unlucky.

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