Troubleshooting PAS sensor

[e.mote]

Hi, I'm an ebike noob trying to fix my brother's ebike, and am looking for some help troubleshooting.

The bike is an Ancheer from Amazon, bought a few years ago. AFAICT, it's a fairly generic bike. 500W rear hub motor (no brand). 36V-18A-450Wh Chinese batt pack.

The trouble started when the rear wheel popped out of the axle, probably because I hadn't tightened it down enough after replace the brake pads. It stretched the motor wiring harness and broke the housing, seen below,



After putting the wheel back in, the PAS stopped working (throttle still works to spin the wheel).

Being a noob, my first instinct was that the wiring damage may have extended to inside the motor. As it happens, we do have a brand-new identical spare motor on-hand, with an undamaged harness, so I swapped out old motor with new motor, keeping the old motor housing of course. Sadly, the PAS still isn't working.

This is the PAS sensor,



Troubleshooting:

. Checked for mechanical wiring & connector breakage, including inside motor controller.

. Checked for physical damage to PAS sensor (none). Cleaned PAS sensor.

. Disconnected both brake sensors to test PAS.

. Disconnected throttle to test PAS.

. Get reading from PAS sensor: from signal pin to gnd is a constant 3V, from power to gnd is a constant 4V. This doesn't seem to change when turning the cranks (and sensor).



All indications tell me that it's a bad sensor, as from what little I know, the signal pin should cycle between 0V to whatever V when the sensor rotates. But I don't know how it could turn bad from a yank on the wiring harness?

This is my first time troubleshooting an ebike, and I have no experience with it, and am hoping the veterans here can lend a hand. So is there anything I'm missing? Is it a straightforward matter of replacing the sensor with this?

https://amazon.com/dp/B07VDQ3GL4

Any suggest or advice would be much appreciated.

PS: This is actually a good experience for me, as I'm working up the motivation to do a DIY ebike conversion, and get my fat ass back on the saddle once more.

Thanks again for any help.

 

[docw009]

PAS sensor is inexpensive. Try another. You might have to make sure the wire order matches.

The PAS cable and motor harness both share that 5V circuit, but since the thrttle (which also uses 5V) and motor work, the 5V must be good. Your 4V is a bit low, but could be your meter. Try unplugging the PAS and check the power and signal with nothing attached.

 

[e.mote]

Hi docw009, I appreciate your input.

With the PAS sensor removed, I got a 4.37V from the power pin. Anyway, I pulled the PAS sensor completely off and tested it with a 5V (4xAA) source, and see if I can get any life from the signal pin with the sensor turning. I got no life. So I'll be ordering a replacement and hope that's the solution.

Fingers crossed. Will report back.

 

[E-HP]

https://amazon.com/dp/B07VDQ3GL4

Any suggest or advice would be much appreciated.

This part of the description is something to keep note of when installing the unit. I'm not crystal clear on what it means, but it does look like you need to do something different when installed on the left or right side.

"Right side installation:Step on the output pulse signal and reverse the step to not output.Left side installation: step forward output pulse signal,reverse step will not output."

 

[e.mote]

Hi E-HP,

Thanks for bringing the pidgin English to my attention. From what I can tell, both right and left side install says the same thing: "step forward" activates the signal, and "step reverse" doesn't.



There's no arrow showing the "forward" direction on the magnet race of the old sensor, so I suppose it's a 50-50 chance of getting it to work, and if not, flip the race and retry?

 

[E-HP]

Yup, pedaling backwards seems like it would confirm needing to flip it if it doesn't work forward, from what I can tell.

 

[e.mote]

Thanks to docw009 and E-HP for their advice. The replacement PAS sensor is indeed the solution. I still don't understand why it fails in the first place. Regardless, at least that issue is resolved. Onto the next one...