Help debugging 0 MPH with Bafang M620 & 860c display

[smorgasbord]

The bike actually works fine, but it always displays 0 MPH.

This is a 3 year old bike, so this used to work. I did just replace the tires, so perhaps I josstled something. I did check that the rear wheel magnet is still attached and is in the right place. Is that what's used to determine the MPH display?

What else should I be checking here?

TIA

 

[Gionnirocket]

Are you moving?
Check distance from sensor to magnet
LED on the sensor illuminating? Does it blink with a magnet pass?
Check the sensor at the connector. Clean straight pins?

 

[smorgasbord]

Yes, moving.
Sensor is close to magnet - closer than on my other bikes, which has the identical drivetrain (but running an EggRider instead of the 860c)
Where is the sensor LED?
Doesn't the sensor connect to the motor, which means I have to take at least the cover(s) off the Bafang motor, right?

 

[Gionnirocket]

LED is at the tip of the sensor opposite the threads

The connection is at the sensor threads

 

[AHicks]

Some of the sensors can be pretty picky as far as magnet location. Lining the magnet up on the center of the sensor may not work. It needs to be on the CORRECT end of the sensor. After that, you may want to check any connections to the sensor, including where it plugs into the motor.

 

[smorgasbord]

My sensor doesn't have an LED.
I checked and the magnet appears strong and is traveling pretty darn close to the sensor.
I opened the motor and the connection seems clean.
Here are some photos:

This used to work. She hasn't ridden in a while and I did change tires, so those are the two factors.

Any other ideas? Should I just try to find a new sensor and replace it?

 

[Gionnirocket]

Without any errors reported on the display or wiring scheme available for the sensor, I'm not sure what other choice you have other than to replace it.
That said I'd guess it's a simple reed device... How many conductors to the sensor?
If 2 you could try shorting and opening rapidly at the connection to the motor (simulating a spinning wheel) to see if it produces a reading at the display. This is just a guess so it may be safer to just replace the sensor

 

[smorgasbord]

Thanks. Of course, it may not be the sensor and could be something in the motor electronics...

 

[AHicks]

Thanks. Of course, it may not be the sensor and could be something in the motor electronics...

Anything's possible of course, but that would be a new one. I think the magnet is plenty close, but if all you've none is a tire change, and it was working beforehand, just for grins, I'd slide that magnet towards the sensor mounting bolt just a hair. As mentioned, I KNOW some of these can be pretty picky.... and it would only take a second.

You pulled the connector apart to verify it looked clean (no green or black)?

3 wires. Positive, negative, and sensor.

 

[smorgasbord]

Yeah, pulled the connector apart and it's all clean.
Repositioned the magnet with no effect, either.
Anyone know where I can buy a Bafang wheel motion sensor? Found one at California-Ebike

 

[Gionnirocket]

That's good, you should have it quickly.
Curious... How many pins/conductors at the connection?
I know it can vary by protocol CAN/UART

 

[smorgasbord]

Looked like 3 conductors. UART

 

[smorgasbord]

Just took the bike out for another short test spin today and noticed that while the PAS levels can be changed on the display, the bike always feels like it's in the top "5" level. Is that also a symptom of not having wheel rotation sensor, or could it be something else?
PS: This is affecting the bike "skipping" in the top 2 gears - see another thread.

 

[Gionnirocket]

With a faulty input anything is possible.
That said it makes sense that it would respond aggressively as the controller is reading the speed as always 0

 

[smorgasbord]

And, it turns out the "30H" on the display is not some 30 hour trip overage, but an actual Bafang error message about a bad connection.
I unplugged the speed sensor and still have the 30H error. Now I guess I need to unplug and replug everything to see what removes the error, right?

 

[Gionnirocket]

30H is a communication error.. to me indicating controller - display or main harness issue
21H is a speed sensor error usually generated when the motor is turning but there's no input from the speed sensor like when the magnet is missing.
But yes I'd check all my connections and replace the speed sensor. You have to start somewhere.

 

[smorgasbord]

Yeah, bike support thinks it might be the controller, and since I have two bikes it's time to swap them. They also suggested using the programming cable to see if that works from the laptop. Both of which I'll try tomorrow.

 

[Gionnirocket]

If you go to the end of the Advance settings in the display... You should see a list of the last 10 error codes.
Not that it'll change anything but there might be more info

 

[smorgasbord]

So, replacing the display seems to have fixed the problem! Lucky I have two of the (mostly) same bikes.

 

[AHicks]

Just curious, but have you tried plugging the display that doesn't work into the other bike?