12V battery charging at elevated voltage (~15.4V) whenever HV system is on, causing warning in ISTA, but no fault codes

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Joined
Mar 8, 2024
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I purchased my 2014 i3 Rex with ~40k a few months ago and I got right to maintenance and tweaking/modding. I did some bimmercode tweaking and that all went fine. However when I hook up ISTA I am getting about 15.4V as reported by the system. I checked with my fluke and confirmed it was about 15.3V at the 12V battery terminals. This triggers a warning in the ISTA program that prevents me from doing some tasks. It pops up as a warning (must be below 14.85V) and blocks me from doing anything in ISTA and I have to close it forcefully sometimes. The voltage is steady. I haven't been able to monitor it while driving, only while sitting (plugged in and unplugged) and the conditions are the same.

When I disconnect the HV system the battery naturally returns to normal ~12V. The 12V battery is from 2022 and shows no sign of degradation that I can see.

All this came up because I wanted to re-program the car to update the software/firmware, but I can't get that far.

So I'm wondering if anyone has seen this or if there is some troubleshooting I can do to investigate further. I do not have any related fault codes or anything for this, the car seems to be fine with it, but I'm suspicious that the 12V charger is set too high or failing to regulate properly.

Edit: My other thought was that the battery was programmed to something different, but it was the standard battery for it. I should mention that I believe it's a DC-DC converter that does this, but I'm not sure where that is in the system.
 
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I get a simular problem using ISTA with a Chinese ICOM, BUT on mine, there is nothing wrong with the car, it is just the ICOM reading a volt too high (15.something). Volt meter shows 14.7 with the DC to DC converter on. I believe ISTA recommends a power supply to keep the 12v (14.5) steady when updating firmware. Maybe that update could be done with the HV battery disabled and your ext power supply adjusted to a level that ISTA won't complain about? Jest an idea.
 
I get a simular problem using ISTA with a Chinese ICOM, BUT on mine, there is nothing wrong with the car, it is just the ICOM reading a volt too high (15.something). Volt meter shows 14.7 with the DC to DC converter on. I believe ISTA recommends a power supply to keep the 12v (14.5) steady when updating firmware. Maybe that update could be done with the HV battery disabled and your ext power supply adjusted to a level that ISTA won't complain about? Jest an idea.
Thanks! That was my plan for the HV if I don't get anywhere on this. I was able to proceed with measurement and stuff with the HV disabled, but then I get all kinds of stray codes from it.
 
Edit: My other thought was that the battery was programmed to something different, but it was the standard battery for it. I should mention that I believe it's a DC-DC converter that does this, but I'm not sure where that is in the system.
The only battery types I've seen in the list of possible battery types for the Battery Type parameter in the Body Domain Controller are flooded-cell lead-acid and AGM, neither of which requires a high voltage for charging.

The DC-DC converter is responsible for providing power to the 12 V system including charging the 12 V battery. It's part of the electric motor electronics (EME) module. I'm not aware of any way to set its output voltage, but I haven't looked into doing this.
 
I purchased my 2014 i3 Rex with ~40k a few months ago and I got right to maintenance and tweaking/modding. I did some bimmercode tweaking and that all went fine. However when I hook up ISTA I am getting about 15.4V as reported by the system. I checked with my fluke and confirmed it was about 15.3V at the 12V battery terminals. This triggers a warning in the ISTA program that prevents me from doing some tasks. It pops up as a warning (must be below 14.85V) and blocks me from doing anything in ISTA and I have to close it forcefully sometimes. The voltage is steady. I haven't been able to monitor it while driving, only while sitting (plugged in and unplugged) and the conditions are the same.

When I disconnect the HV system the battery naturally returns to normal ~12V. The 12V battery is from 2022 and shows no sign of degradation that I can see.

All this came up because I wanted to re-program the car to update the software/firmware, but I can't get that far.

So I'm wondering if anyone has seen this or if there is some troubleshooting I can do to investigate further. I do not have any related fault codes or anything for this, the car seems to be fine with it, but I'm suspicious that the 12V charger is set too high or failing to regulate properly.

Edit: My other thought was that the battery was programmed to something different, but it was the standard battery for it. I should mention that I believe it's a DC-DC converter that does this, but I'm not sure where that is in the system.
Your battery should read min.12.6v at rest.if it does,perhaps a battery reset via insta (?) might do it
 
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