M400 36V motor not working anymore (does not turn on at all)


New Member
Hi everybody,

first of all thank you for accepting me as a new member! I enjoyed reading the discussions. I now have a problem, I could not find an answer for in the forum.

I have a cargo bike with a M400 36V motor connected to a DPC18 dispaly. Everything was working fine until recently. I had the rear wheel exchanged (completly new gear shift etc.) and due to a lack of time I did not do it myself this time. Now the BAFANG system is complety dead. When I try to switch it on, the display stays completely black (not even a glimpse). Here is what I have done so far for trouble-shooting:

1) I measured the battery (36 V) and it puts out 42 volts on the connector cable.
2) On the display connector I get a reading of 36 V "only". Interestingly this reading drops only very slowly after disconnecting the battery, so there must be some capacitor loaded (not sure this information is relevant, but I thought I include it anyway)
3) Since there was voltage on the display connector I ordered a new DPC18 display, but this is also not working.

My guess now would be a faulty controller, and I am about to order a new one. However, they seem to be difficult to find (I mainly find 46 volt controllers).

Does anybody have suggestions on further trouble-shooting or a good source to get a new 36 Volt controller for the M400? I am located in Europe.

Thanks a lot!
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greenbikekit has them, anna is great and might have some suggestions to check
you may also be able to upgrade to a 350 watt controller if yours is 250

this sucks and i am not sure what to tell you , maybe some of the other bafang mid drive guys will chime in

wondering about a fuse in the battery blown??? think i would check for that first
or something unplugged

have you checked all the pins on the motor plug and anywhere else they might could have gotten bent, not sure how someone screwed it up doing a rear wheel

hope you figure it out and dont need a new controller
keep us up to date
Hi Vincent, thanks for your reply and the suggestions! I am also not sure that this is really connected to the rear wheel change. Maybe this was just a coincidence.

I don't think it is the battery, since it puts normal voltage (42 Volt reading on a 36 Volt battery is normal, or?). I can measure the same current also on the connector towards the motor. I am currently checking all connections to see whether there is something loose!
I have question concerning the controller. You mentioned upgrading to a 350 Watt. Can I just swap my 250 Watt for a 350 Watt one? Or do I then also need a 46 Volt battery?
Thanks again!
No the 350 can be run on 36 volt

I’m not an expert on this, talk to Anna at Greenbikekit, she should be able to help you if it’s the controller and I’m thinking maybe she would know a way to test it…???

They were great to work with

Where do you live? I am intending to change my 250 out to a 350 and I might sell the 250 watt controller, I had not planned to but I don’t really care that much

Unfortunately I won’t get into this project for a couple of weeks
Thanks again! I contacted Anna at Greenbikekit today!

I live in the south of Germany. Since we use the ebike for commuting it would be good to get it back working as soon as possible. i think I will order one from Greenbikekit. But thanks for the offer!
I will! She advised me to get an EB-BUS cable in addition, since this could also be faulty. I ordered both and will update you here once the stuff arrives and I can replace the parts (however this will take a week or two)!
It worked! I replaced the controller today (ordered a new 250W from Greenbikekit) and it turned on. So the display is intact as is all the wiring. Looks like it was indeed a faulty controller. Pedal assist etc. is as before!
Many thanks again for your help!