Bosch CX Gen 5 Smart System – Motor with momentary power losses

[António13_PT]

I have a bike with a Bosch CX Gen 5 motor ( 34 T chainring ), and and since I took a trip with panniers, the engine has been experiencing momentary power losses.

When I ride in the lowest gears and on steep climbs, therefore slowly, the motor would lose assistance for a quarter of a second, or less, and then recover, but the sensation in the legs is unpleasant

On gentle climbs, or when riding faster even when pushing the motor, it never did that

On certain occasions, when riding with a higher level of assistance, for example Sport, after this quick cut, it seemed to switch to Tour mode, and I had to change the mode to Tour and then back to Sport to recover the Sport assistance.

It has already been to the shop for general servicing, and they did not detect any faults.
The electrical connections appear to be fine
I have all the software updates done

Can anyone help me figure out if this is just a software issue or if it could be a malfunction ?

 

[António13_PT]

After a ride of more than 120 km and over 3000 metres of vertical climb, where I paid attention to what was happening and changed some options in the Flow app, the situation was as follows :

The motor does not lose power, it switches off and then switches back on again, as when we ride slowly and with little cadence and force on the pedals.

I increased the dynamics to +5, which reduces the number of times the motor switches off, but does not eliminate it.

This only happens when going uphill and relatively slowly.
When riding fast, the problem does not occur, which I think rules out the possibility of a bad or dirty electrical connection.

So I think the most likely cause is a sensor that is not fast enough to send a signal and has some kind of problem.

Can anyone help with what it might be, or at least point me in the right direction?

 

[António13_PT]

After sending the bike to the shop (Bike Discount) under warranty, where they replaced the Purion 400 cable – which was pinched – they charged me nearly 300 euros and the bike came back exactly the same

A whole month without a bike for this... They didn’t even test it under the conditions I’d described
Now they say they can have another look and charge me again (I was very angry with this response)

Meanwhile, the speed display has started showing erratic speeds, and I’d never noticed that before.
The problem isn’t a loss of power; the motor cuts out when it exceeds the 25 km/h limit.
When I increase my speed, this stops happening.

Video showing the GPS speed ( 6,2 ~ 6,3 km/h ) and the speed on the display ( 5,9 ~23 km/h )

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What could be causing this ?
Motor fault ? Sensor ? Magnet ? Something magnetised ?

 

[Plummet]

After a ride of more than 120 km and over 3000 metres of vertical climb, where I paid attention to what was happening and changed some options in the Flow app, the situation was as follows :

The motor does not lose power, it switches off and then switches back on again, as when we ride slowly and with little cadence and force on the pedals.

I increased the dynamics to +5, which reduces the number of times the motor switches off, but does not eliminate it.

This only happens when going uphill and relatively slowly.
When riding fast, the problem does not occur, which I think rules out the possibility of a bad or dirty electrical connection.

So I think the most likely cause is a sensor that is not fast enough to send a signal and has some kind of problem.

Can anyone help with what it might be, or at least point me in the right direction?

Are you running in eco+? becuase this is exactly what eco+ does. It turns off to conserve battery at low pedal pressure and turns back on when higher pedal pressure is excerted. Change the mode to eco and you will be back to standard operation.
Expect faster battery usage if eco is being used.

 

[bmwpowere36m3]

My Norco Range VLT with CX gen 5 does the same in tour+ mode occasionally... I wouldn't say super slow cadence, but usually technical climbing when pausing is required for a second or two and followed by pedaling again. Upon reapplying pressure to the pedals it feels like the motor is off (no assistance) and it can take a full crank to kick in again. Way longer for assistance to kick-in than when the bike is operating "normal".

I haven't noticed or recall it happening in the other modes. Maybe eMTB, but even less frequently. Then again, I spend most of my time in those two modes. The glitch has never caused the assistance modes to switch and I rarely pay attention to the speed readout on the display.

My first thought was the motor isn't getting a good reading from the magnet, but assistance should kick in as soon as there's pressure on the pedals. Its odd and it happens randomly and infrequently... however super annoying when it happens because it can near stall you or making advancing on a technical climb very difficult till the motor kicks in again.