HVBJB in cold weather

[noclue41]

So, I just blew the 3rd HVBJB on my ‘21 GT in the past year. Almost a year to the day on the first one I did. (Four total, one before I owned it was not replaced with the revised part). Each time I popped it the weather was quite cold, I had pushed it to full power in Unbridled, and the battery was cold and not fully preconditioned. I’ve had no problems with full throttle in the summer.

I wanted to pose a theory to the forum. Is it possible that a cold battery is delivering lower than expected voltage at full power and triggering the ‘Sevice Vehicle Soon/Reduced Power’ software protection that was released before the new parts? And the HVBJB is really not faulty? All three have been the revised part, LK9Z-10C666-C. Or did I really pull a dumb and damage the part?

Luckily, I happen to have an appointment for another issue, but I am wondering if I ask the dealer to simply clear the error. Then just ensure I don’t do full power on a cold battery until it is above freezing.

I’ve seen some similar posts about cold weather and the original part on the ‘21s, so it got me thinking.

Appreciate any input!!

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[Mach-Lee]

The Service Vehicle Soon/Reduced Power warning message means an excessive voltage drop across the contactors under load has been detected. That will not just occur because the battery is cold. It means there is actually a bad connection inside the contactors.

If you want to clear codes and tempt fate thinking it's an intermittent issue in the cold, that's your prerogative. If the SVS error returns again, then HVBJB should be changed. FYI you can continue driving the car with the SVS error and power limit active until the replacement. But if the contactors are bad, it could one day fail as a Stop safely now and refuse to move.

If anything, it's possible the cold is causing problems with the contacts seating fully on startup. But that's just a theory. To minimize problems, plug in every night so the battery stays warm. A warm battery may also make it less likely for the contactors to stick and make bad contact.

 

[noway]

If the contactors is not fully closed and heat up because of high resistance they will be damaged as a result, so having it replaced when it happens under warranty is probably a good thing.

I would think it is possible that low 12V voltage could cause the contactors to not have the full closing power as they would normally which could cause them to have slightly higher resistance than the software calculates them to have, but this would damage them over time

It is not uncommon for faults to present themselves during cold weather since that is when mechanical parts move slowest, but it does not mean the fault is caused by the cold, just that it showed up earlier

 

[Mach-Lee]

I would think it is possible that low 12V voltage could cause the contactors to not have the full closing power as they would normally which could cause them to have slightly higher resistance than the software calculates them to have, but this would damage them over time

Contactor coil holding current is PWM controlled which will compensate for voltage differences.

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