Help understanding a HVJB Repair

[dan_meh]

Following up on this thread: https://www.macheforum.com/site/threads/when-car-bricks-what-hvb-report-should-i-expect.44392/

I have photographed the invoice and manufacture plate of vehicle.

Here’s what the technician told me (paraphrasing):

• It was a fuse inside the high voltage junction box. Usually, it’s not the fuse that goes bad.
• I put in a new version of the HVJB. [I asked him if it was a newer version than the original equipment].
• The 12 volt failed because the HV battery failed. [I suspect it is because it was parked at the dealer for a long time and had to be messed with to get a tow?]

Some things I would like to understand to trust the vehicle:

• What do you see in all the codes?
• Is it true that Ford released a new HVJB between my car’s manufacture date and now?
  • Another way to ask it: if the old one failed, and they just put in the same part, should I trust it?
• Does the fuse failure implicate the HV battery?
• Can anyone think of a reason why the DC-DC module would go bad? Technician didn’t know

Thanks in advance!

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[HuntingPudel]

I do not see a part number for an HVBJB. I do see the high voltage converter, fuses, coolant, etc. So it appears that they did not replace the HVBJB. Note that the most recent revision to the HVBJB that took place was in late November of 2023, so your car should have the current revision as built. ??

I believe that your 12V battery lost charge due to the HV fuse being blown and the DC Converter being borked, which would prevent the DC-DC converter from kicking in to charge the 12V battery. You likely didn't need the new 12V battery, but it's not a bad practice to replace an AGM battery after it's gone to no voltage. ?‍?

 

[dan_meh]

Thank you @HuntingPudel !

Maybe I misunderstood the technician when he was talking to me, but I swore he said that he replaced the “old version of the HVJB with a new version of the HVJB.” I thought that was weird because I thought all ‘24s came with the new and improved unit.

Once isn’t a pattern - maybe it was a manufacturing defect? - but I won’t be road tripping this car for a while to see if it reoccurs. My layperson understanding of fuses is that they blow because of overcurrent. I don’t know and the dealer couldn’t tell me if there was an overcurrent event and if so, the cause.

 

[Mach-Lee]

There must have been some kind of fault in the DC/DC converter module that blew the high voltage fuse powering it. The HVBJB is also the fuse box for the high voltage system. They simply replaced the 50A fuse that blew (twice because they did not identify the fault in the DC/DC the first time) along with the faulty DC/DC converter.

The fuse they replaced is circled in magenta, it just pulls out:

You already have the newer version of the HVBJB in a 2024, so they didn't need to replace the whole HVBJB, just the fuse.

The DC/DC going bad is rare, nothing to worry about now.

 

[dan_meh]

Thank you @MachLee !

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