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2022 Ioniq 5 Premium 73kW
135 Posts
Steps to reproduce:

1. Discharge the battery down to 34%. (possibly not necessary, I did this because I was investigating if battery saver activates under 35% SOC)
2. Wait until the battery saver feature activates. (timing may be important, it may trigger in a narrow window of time)
3. Plug the car in to charge on AC power

Outcome: The traction battery will charge on AC power WITHOUT ENABLING THE +12 DC-DC CONVERTER! This will quickly drain it dry (looks like in about 2-3 hours it will be dead)

I have 2 theories how this happened. One is :
Event Plugged In -> Disable Battery saver -> Disable +12 DC-DC Converter
Event Plugged In -> Enable +12 DC-DC Converter.

One way this could happen is there are 2 control messages hitting the CAN bus at the same time and one is masking the other. (meaning the firmware does one and ignores the other, because it has no queue and when executing a state change is 'locked out' from any further commands to the contactor board)
The other way this could happen is if they are using a state machine, and this particular combination of states and state transitions: (while battery saver, initiate charging) is improperly handled. Less experienced firmware engineers don't write explicit state machines but have an implicit one in their code with various state variables and a mess of branch statements, this could be why.

About me: I have about a decade of experience in embedded control systems, a couple years working for an automotive tier 1, and I currently work on ADAS systems for a tech giant. I am not an expert in 12 battery charging logic but I have done various related systems in the past. Typically asian OEMs ignore messages from users, they would have to find this bug themselves, but maybe the Ioniq guy or someone big can replicate this bug on youtube and get their attention.

If someone knows the Ioniq Guy or Out of Spec Review's screenames on here can they ping them?

The below pictures: the first is my log showing the smoking gun failure. The second is showing that 12.13 volts is extremely bad, i am still waiting to see if it fails or saves itself at the last moment but I think it's about to fail. And finally is a picture confirming that the car IS charging, exactly at the same time when I took these logs the car thinks it is charging.

Other users have complained of failures in a similar situation, and said they took it to the dealership and got a new lead acid battery. That is NOT THE PROBLEM and WILL NOT FIX IT. This will keep happening until there is a software patch for the actual bug.

View attachment 43337

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Update: it failed to fail. Hyundai let it do damage to the 12V battery but at 9 volts it activated some kind of failsafe:
View attachment 43349
looks to be resolved now with a BMS update

Got an IONIQ 5? You need the BMS update. - YouTube
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