Bosch Gen 4 Speed Sensor

[Husky430]

My Bosch speed sensor (I'm guessing that this is the cause of the problem) seems to be playing up.
When I start a ride and get into it and hold a high speed, somewhere over 20kph, my speed fluctuates up and down on the speedo causing the motor assist to cut in and out.
Seems to settle down when I get into the ride a bit more but again if I find myself on a fast fire road and get the speed up it will occur again though not all the time.
Nothing worse than an intermittent fault.
Just wondering if others have had this, or a similar problem, at the moment it's just annoying, but worried that it could become worse or cut out entirely.

 

[Bear-uk]

My Bosch speed sensor (I'm guessing that this is the cause of the problem) seems to be playing up.
When I start a ride and get into it and hold a high speed, somewhere over 20kph, my speed fluctuates up and down on the speedo causing the motor assist to cut in and out.
Seems to settle down when I get into the ride a bit more but again if I find myself on a fast fire road and get the speed up it will occur again though not all the time.
Nothing worse than an intermittent fault.
Just wondering if others have had this, or a similar problem, at the moment it's just annoying, but worried that it could become worse or cut out entirely.

It will cut out if it can't detect any speed because the motor thinks it's stationary.
In the past I've had to stick a washer between frame and sensor too make the gap smaller so it gives a better signal.
If that's no good then put a new speed sensor on as there easy enough to change.

 

[jayx4]

Mine exhibits that behavior as well, but I attributed it to the motor being designed to cut off after reaching a specific speed

 

[Mackeminexile]

Mine cuts regularly and I've narrowed it down to a loose connection at the motor. Have replaced the magnet etc. Wiggling the wire at the motor end (Orbea Wild) seems to work. Keep meaning to drop the motor and replace the wire but never seem to have the time.

 

[Stihldog]

If you’ve reached your country’s assist level (32khr NA or 25khr EU), it will feel as though you’re dragging an anchor.

If you’re bike behaves like this, before you reach the assist limits, then it’s likely electrical issues with the battery, speed sensor or motor connections.

A LBS may be able to quickly diagnose the issue once they download the data.

Based on your description I would start by insuring that your battery is secure and making good contact with the connection. (This has happened to me). A specific vibration can trigger this effect.

The speed sensor or magnet position. The sensor is usually a contained reed switch. Two wires send a signal to the motor, which indicates motion and speed. The sensor can fail or become intermittent.

It’s difficult to replicate trail conditions so your investigation may involve trial and error. Perhaps data acquired from your LBS may help narrow down the problems.

Sometimes it’s like searching for a creaking noise …

My bike would loose power (weird Kiox behaviour) on a specific fire road at a specific spot. Another bike behaved differently at another spot. The frequency of vibrations may be difficult to replicate outside of trail conditions, but it may be detected from the data input.

 

[Husky430]

If you’re bike behaves like this, before you reach the assist limits, then it’s likely electrical issues with the battery, speed sensor or motor connections.

Thanks for the replies fellas and interesting to see I'm not on my own with the fault.
Yeah this is what's happening and you can actually see the speed jump/cycling up and down on the speedo rather rapidly, usually when I'm in the low 20's kph and it seems to settle down once your at a consistently slower speed or once the motor/electrics have 'warmed' up?
Will take it to the shop as it's almost at 5000km now so due for a service and get them to hook up their computer to hopefully see what's occuring.

 

[Tribey]

I had the same symptons on my Whyte. Supplying LBS checked it out and replaced the speed sensor under warranty. No problems in the 3 years since.

 

[ValActionT 750]

Cracked me up at the comparison to creaking noises. I thought I was once again chasing dreaded Cube head set creaking. LBS found that I had not snapped the battery in completely.

 

[Paul F]

My Bosch speed sensor (I'm guessing that this is the cause of the problem) seems to be playing up.
When I start a ride and get into it and hold a high speed, somewhere over 20kph, my speed fluctuates up and down on the speedo causing the motor assist to cut in and out.
Seems to settle down when I get into the ride a bit more but again if I find myself on a fast fire road and get the speed up it will occur again though not all the time.
Nothing worse than an intermittent fault.
Just wondering if others have had this, or a similar problem, at the moment it's just annoying, but worried that it could become worse or cut out entirely.

If it is the sensor. Then clean it at the wheel and where it connects into the motor. You will have to take the motor cover off. Not big deal.. Or it could be the software that restricts the motr at 15.5mph that is at fault. If this is the case only yourBosch bike shop can fix that. Then fit a delimiter.