Yamaha PW-ST Motor Jerky

[E-bobby]

Hi guys, quite new to e-bikes, hopefully somebody can help me out, I recently purchased a haibike hardseven and it had a issue with it, Here are some of the symptoms that are happening;
Odometer flashing
Speed staying at 0kmph
Motor kicks in for a second then does not give any power, same with walk mode, I hold the button and it starts to go, then stops, then goes etc. I have done a little research about this and i found that these are the symptoms of a speed sensor issue (as ChatGPT says), so i tried moving my magnet closer as it is quite far away to be honest, (see pic) no difference, I tried using a fridge magnet and slowly going past to act as if the wheels moving, again, nothing, I took the motor out and reached the speed sensor connector, looked fine inside, bit of dirt but nothing concerning, plugged it back in and it clicked so it was definitely in securely, again no difference, same issues, I read that there is some sort of menu for the error codes when you hold the + and - button but nothing worked for me.
any help is appreciated.

 

[JoeCrow]

The symptoms you describe are indeed typical of a faulty or misajusted speed sensor. Given your trouble shooting I think it is most likely a defective sensor so would suggest taking it to your LBS for repair. My wife's Cube had an identical problem the repair cost 80 Euro most of that was labour apparently it can be a real pita to lay the cable in.

 

[E-bobby]

The symptoms you describe are indeed typical of a faulty or misajusted speed sensor. Given your trouble shooting I think it is most likely a defective sensor so would suggest taking it to your LBS for repair. My wife's Cube had an identical problem the repair cost 80 Euro most of that was labour apparently it can be a real pita to lay the cable in.

That’s great to hear, thank god it’s not a motor issue , I’ll find out what sort of speed sensor is on it and I’ll order one and try and fit it myself, I basically had it off today just needed one bolt. Thanks for the reply Joe!

 

[JoeCrow]

Let us know how it goes. On my wife's Cube the cable runs through the frame to the Bosch motor.

 

[E-bobby]

Let us know how it goes. On my wife's Cube the cable runs through the frame to the Bosch motor.

Oh yes I can imagine that’s very hard to fix, mine is just from the back wheel into the motor under the crank, it’s just 3 big bolts and 2 little Alan keys, internal cabling is quite tricky. Thanks for your help joe. I’ll keep you updated, all the best

 

[matthewslack]

The magnet also needs to pass the correct part of the sensor. On Shimano, that is the top end of the straight bit, before the round bit for the mounting screw. Yours has a groove about there - that might be indicating the spot.

The distance looks quite large, but that might be the picture. Washers to space out the sensor can close the gap if needed.

Behaviour matches Shimano behaviour: torque turns motor on, but not for long if no speed signal detected.

 

[E-bobby]

The magnet also needs to pass the correct part of the sensor. On Shimano, that is the top end of the straight bit, before the round bit for the mounting screw. Yours has a groove about there - that might be indicating the spot.

The distance looks quite large, but that might be the picture. Washers to space out the sensor can close the gap if needed.

Behaviour matches Shimano behaviour: torque turns motor on, but not for long if no speed signal detected.

Hi there thanks for the reply, I have just tried using a magnet to see if it shows any speed and it still doesn’t unfortunately. Would I have to be pedaling at the same time for it to show this? Thanks for the help mate, cheers

 

[E-bobby]

Hi guys just took the sensor off the mounting bit, only thing I can see wrong is that there is a crack where someone had tightened it too much

 

[matthewslack]

A crack in the mounting hole makes no difference. A crack through to the sensor could well be the problem.

A magnet passing a working sensor repeatedly should generate a speed display, but it will not make the motor work. Your spoke magnet will do: just wave it past the sensor nice and close once or twice per second somewhere near the perfect place and distance and the speed display should show something more than zero.

If not, new sensor and try again.

 

[E-bobby]

A crack in the mounting hole makes no difference. A crack through to the sensor could well be the problem.

A magnet passing a working sensor repeatedly should generate a speed display, but it will not make the motor work. Your spoke magnet will do: just wave it past the sensor nice and close once or twice per second somewhere near the perfect place and distance and the speed display should show something more than zero.

If not, new sensor and try again.

Yeah I’ve tried that, I did 3 different magnets just to be sure lol, I took the sensor off the bike but still connected inside, waved the normal one off bike, at different distances and had someone check the display, nothing, I used a fridge magnet and a strong one to test this, still nothing, I’ll look at a couple now I’ve seen one for 45 with the new magnet as well, (mines perfectly fine but I’ll just use it). Alls I’m worried about is it being the other wire that connects to the ecu I think. Is it possible for it to be that? Thanks for your help Matthew

 

[matthewslack]

Yeah I’ve tried that, I did 3 different magnets just to be sure lol, I took the sensor off the bike but still connected inside, waved the normal one off bike, at different distances and had someone check the display, nothing, I used a fridge magnet and a strong one to test this, still nothing, I’ll look at a couple now I’ve seen one for 45 with the new magnet as well, (mines perfectly fine but I’ll just use it). Alls I’m worried about is it being the other wire that connects to the ecu I think. Is it possible for it to be that? Thanks for your help Matthew

I don't know the Yamaha like I know Shimano, but it may be just as simple. One big connector from battery to motor and two small wires from speed sensor and to display. The controller is inside the motor.

Your symptoms point to speed sensor, I wouldn't worry about anything else until you've tried a new one.

 

[E-bobby]

I don't know the Yamaha like I know Shimano, but it may be just as simple. One big connector from battery to motor and two small wires from speed sensor and to display. The controller is inside the motor.

Your symptoms point to speed sensor, I wouldn't worry about anything else until you've tried a new one.

Alright mate I’ve ordered a new one, should be here Wednesday, thanks for your help . Cheers

 

[chris_n]

The centre of the magnet should pass the groove in the sensor near the mounting point. Yours is way too far from the centre of the wheel.