2020 Internatinal CE brake booster runs continously with battery switch off

[Mattyg17]

We got a 2020 international ce school bus with a hydromax brake system.
The booster runs constantly, also intermittently, even with key off, and battery switch off. It is currently well below freezing where we are from.

We have swapped the relay, brake switch, and installed a new pressure sensor on booster.

I was able to have it continously run by lightly hitting brake pedal and thought we had it solved after swapping brake switch because I was not able to make it run continously after swapping brake switch.

Parked bus outside on lot, shut battery switch off, came back next day and went outside to bus and booster is running, and had to boost the bus to start it.

Wondering where to go next as our service information is very limited.

Possible internal issue with booster?

[bbkid]

I'm no bus mechanic, but the simple fact that you turned the battery switch off and the system continued to operate electrically overnight makes me pretty curious. My instinct at that point is to look deeper than the booster itself, but i also don't know whether the electric brake booster should apprently be bypassing the battery cutoff or not.

Also, since most folks on this site are working with far older busses for personal use, and there aren't too many fleet mechanics around, I'm not sure how much experienced help there is to be found here. With how most manufacturers are getting in regard to service info, i totally understand reaching out wherever you can though...

This a fleet vehicle? Even with things being as they have been with "right to repair" and everything, it's crazy if the dealer wouldn't at least try to help troubleshoot a schoolbus that new that's being used for its intended purpose. I worked for a JD dealer for a while and even we didn't give customers that kind of cold shoulder... (and i saw first hand how it could be getting info out of corporate... sad when a servicing dealer can't get basic dtc info for a $120k machine just because it wasn't from a line we actually sold)

Either way, good luck trying to get usable service info! It feels like you struck gold when (or more increasingly: "if") you finally get it sometimes, and for good reason...