Cube Nuride Bosch PowerTube 750 Temperature too high error

[Oleophobic]

This is a repost from my other thread, just to check if the bot can help:

I have a Cube Nuride (Bosch Performance Line CX Gen4 and Bosch PowerTube 750Wh) that’s throwing errors whenever the motor uses more than 180-190W (by my estimation) and shuts down the whole system (orange LED blinking), reporting error 680008.
However, the battery only has 94 cycles and the battery is cool (I literally take the bike out of the basement in which it has been sitting in for 50+ hours at 20°, start riding, and the error is thrown in less than 10 seconds if I pedal hard).
I’ve tried resetting the battery (holding the button on it for a while), I’ve tried unplugging and plugging all the connectors, I’ve even cleared the diagnostic codes using my friend’s Bosch diag, but to no avail.

The bike is out of warranty, and I’m not financially able to replace the battery.
I’m skilled in electronics and repairs so I’m happy to open up things, resolder components, rebuild cables/connectors or even reball chips if needed.
The main issue is that I have no idea where to start, and I hate Bosch for being so locked down and unfriendly to repairs. I’m aware that almost every hardware issue is handled by replacing the whole thing by Bosch, but this isn’t a route I’m willing to go with.

 

[Greg Watts]

This is a repost from my other thread, just to check if the bot can help: I have a Cube Nuride (Bosch Performance Line CX Gen4 and Bosch PowerTube 750Wh) that’s throwing errors whenever the motor uses more than 180-190W (by my estimation) and shuts down the whole system (orange LED blinking), report...

@Oleophobic - error 680008 on a Bosch Smart System is a battery protection trip, specifically a thermal or current-limit fault. The fact that it triggers within 10 seconds on a cold battery at low cycle count is the important clue here: it's almost certainly not the battery cells themselves (those would need to be warm and stressed to genuinely overheat), but rather a faulty NTC thermistor or BMS sensor inside the battery reporting a false temperature.

The Bosch BMS trusts its own sensor completely. If one NTC is reading 60°C when the actual temperature is 20°C, it'll shut down immediately and confidently. It doesn't care what you feel with your hand.

Where I'd start if I were poking around inside: • NTC thermistors - there are typically several embedded in the cell pack. A failed or drifted one will false-trigger thermal protection. These are standard NTC bead thermistors and can be tested with a multimeter (resistance at room temp should be predictable from the part's B-value curve). A shorted one will read near-zero resistance = very high temperature to the BMS.

• BMS connector/ribbon - the interface between the cell sensing harness and the BMS board is a common point of failure. Corrosion or a hairline fracture in a flex cable can cause a single cell group or sensor to read wildly.

• The BMS board itself - less likely at 94 cycles, but not impossible. A failed comparator or ADC channel will misread sensor data.

What makes this tricky: Bosch's BMS firmware is signed and the pack is fully proprietary, so you can't reflash or recalibrate the sensor mapping. You can only fix the hardware the firmware is reading. The good news is that NTC thermistors are cheap generic parts; the bad news is finding which one is drifted without a reference schematic.

Practical next step: If you can open the pack (some Bosch PowerTubes use T20 Torx under the label - worth checking), read each NTC with a multimeter at room temp. At 20°C a typical 10kΩ NTC should read roughly 12 - 13kΩ. Anything wildly off is your culprit.

Worth documenting as you go - there's very little public teardown data on the 750Wh PowerTube specifically, and this forum would benefit from it.

 

[cream]

Wow, great answer @Greg Watts

It's also important to point out another NTC parameter, Beta factor. Most batteries/BMS boards I serviced were using 10k B3950 type NTC sensors. Either bead or SMD.

I think I encountered this fault on a Bosch smart 750 batteries some years ago. The BMS has 4x temperature sensors. Two of them on the cells the other two on the board, near the Mosfets (top/bottom). The onboard sensors are 0603 10k B3950. Unfortunately I don't have photos of the BMS board for exact location.

Worth to note it took some time to solve this because Bosch diagnostic tool is misleading. It will only show one temperature value which is actually a processed version derived ONLY from the cell NTC sensors. Mosfet/board sensors are not shown in live data or history memory (lowest/highest temperature recorded). Such a pitty!

 

[Greg Watts]

Wow, great answer @Greg Watts It's also important to point out another NTC parameter, Beta factor. Most batteries/BMS boards I serviced were using 10k B3950 type NTC sensors. Either bead or SMD. I think I encountered this fault on a Bosch smart 750 batteries some years ago. The BMS has 4x temperatur...

@cream - that's a genuinely valuable addition, thank you. The Beta factor point is one that trips up a lot of DIY troubleshooters who assume all 10k NTCs are interchangeable. They're not - two sensors with the same nominal resistance at 25°C but different B3950/B3977/whatever Beta values will give meaningfully different readings across the operating range, and a BMS that's calibrated for one will misread the other.

The four-sensor architecture is interesting and I wasn't aware of the exact split on the Smart System 750 BMS specifically. Two on the cells, two near the MOSFETs - that makes sense thermally; the FETs are your highest-dissipation point during high-current discharge, and they'll spike well before the cells do on a hard climb.

The diagnostic tool blind spot you've identified is a real gotcha. If the Bosch tool only surfaces a processed value derived from the cell sensors, and the MOSFET sensors are what actually tripped the protection, you could have a healthy-looking cell temperature reading right up until the moment the system shuts down. That would make it look like a mystery fault rather than a straightforward thermal cutoff - which is almost certainly what confused the original poster's Cube diagnosis.

As Tom Sellers notes, the BMS in these packs is responsible for protecting cells that may have failed or degraded - but as you've pointed out, the diagnostic window into board-side thermal events is essentially opaque from the standard tooling.

(@Tom Sellers's post) Given your background servicing Specialized packs - have you found the MOSFET sensor placement consistent across BMS revisions on the 750Wh Smart System batteries, or did Bosch move them between board revisions? That would be useful context for anyone trying to probe those sensors directly.

 

[cream]

Bms board and temperature sensors from a 750wh Bosch smart system powertube. Don’t know if there are major hardware revisions, I don’t deal with Bosch batteries too much.

 

[Greg Watts]

187325187326 Bms board and temperature sensors from a 750wh Bosch smart system powertube. Don’t know if there are major hardware revisions, I don’t deal with Bosch batteries too much.

@cream - those photos are gold, thank you for posting them. That's exactly the kind of primary evidence this thread needed.

Looking at the BMS board shots: the sensor placement is clearly visible, and it confirms what you described - the onboard NTC sensors near the MOSFETs are discrete SMD components, physically separate from whatever's buried in the cell stack. The board layout looks fairly clean for a pack that has to survive the inside of a down tube on a rough trail.

On your question about hardware revisions - completely fair to say you don't deal with Bosch batteries as often as Specialized. Given your background pulling apart Levo packs, the architecture here probably looks familiar in principle (cell NTCs for SoC and thermal modelling, board-side sensors for FET protection) even if the exact BMS is different. Bosch's integration is notably more locked-down than the Specialized BMS ecosystem you've been working in.

The practical takeaway for anyone following this thread is now very concrete: if you're chasing error 680008 on a Smart System 750, the diagnostic tool is showing you cell temperatures only. The FET sensors that may have actually triggered the shutdown are invisible in the standard Bosch tooling. You'd need either a BMS-level communication tap or a direct NTC probe on those 0603 sensors to know what temperature the board actually reached.

As for whether Bosch revised the board between production runs - I genuinely don't know, and I'd rather say that than guess. If anyone else has a second 750Wh BMS to compare against these photos, that'd be worth posting.

 

[Oleophobic]

Wow, great answer @Greg Watts

It's also important to point out another NTC parameter, Beta factor. Most batteries/BMS boards I serviced were using 10k B3950 type NTC sensors. Either bead or SMD.

I think I encountered this fault on a Bosch smart 750 batteries some years ago. The BMS has 4x temperature sensors. Two of them on the cells the other two on the board, near the Mosfets (top/bottom). The onboard sensors are 0603 10k B3950. Unfortunately I don't have photos of the BMS board for exact location.

Worth to note it took some time to solve this because Bosch diagnostic tool is misleading. It will only show one temperature value which is actually a processed version derived ONLY from the cell NTC sensors. Mosfet/board sensors are not shown in live data or history memory (lowest/highest temperature recorded). Such a pitty!

This is incredibly useful info, and thanks for the photos! It’s possible that the MOSFETs went bad so I’ll have to check that as well.
I’ll make sure to post a teardown and guide (if I suceed) in my original thread and here once I open it up.