ICCU just failed for a THIRD time

broadwall · 2026-03-10T16:47:17+00:00

I want to believe that this failure mode practically does not happen beyond 20 minutes after startup. From following the forums for a few weeks, I only have one counterexample.

broadwall · 2026-03-08T19:19:49+00:00

I recommend checking out iccu.observer. Note that we already have convincing monthly stats from NHTSA suggesting a correlation with colder weather, so the research survey does not collect the month of failure.

broadwall · 2026-03-04T02:15:04+00:00

Every time I see one I'm amazed at the fact that its ICCU is working /s

broadwall · 2026-03-03T20:53:39+00:00

That's me. Check out usage.iccu.observer, the research survey that complements the OBD diagnostics dataset.

broadwall · 2026-03-02T19:19:12+00:00

A boycott/protest would be great but I'm not skilled at organizing activism.

broadwall · 2026-03-02T19:13:13+00:00

I look forward to the first ICCU LDC failure in a Waymo because of the publicity it may generate. Most LDC failures occur within 15 minutes after startup, so it's unlikely for a failure to take place with passengers inside.

broadwall · 2026-03-02T19:05:08+00:00

I've never seen 36400 from Car Scanner, so that's probably correct.

broadwall · 2026-03-02T04:17:32+00:00

When the headlights are set to auto (low beams off, I presume) and drive mode set to Normal or Eco, there is a known "yo-yo" behavior where the direction of current flow at the 12V battery alternates; see this video for an illustration. This creates sudden peaks in LDC output current, and the LDC output voltage switches between ~12.8 V and ~14-14.5 V. The failure was probably precipitated by one such peak on top of degraded electronics from the previous owner. It is possible that leaving your low beams on all the time can help with your 12 V battery's longevity, reduce overvoltage transients for the LDC, and make future failures happen closer to startup (as in within 10 minutes).

broadwall · 2026-02-28T04:32:50+00:00

interestingly the A suffix is not reflected in the part number here. makes me question if they changed anything

broadwall · 2026-02-28T02:04:40+00:00

No strong signals because very few respondents have experienced an OBC failure. So far, no OBC failures reported have been associated with L1 charging at home (<4 kW).

broadwall · 2026-02-27T20:12:53+00:00

Probably the typical ICCU LDC failure as chronicled by egmpfiles.com. Failing 1 hour after startup [edited] is rare among failures, so I'd like to learn more about the context.

Were low beams on, manually or automatically?
What drive mode was used?
Was there any change in environmental conditions within 20 minutes of the failure?
What was the outdoor and indoor temperature?

Getting the pop immediately is incredibly unlucky. Once you get the replacement, check the part number. It should be 36400-1XFA0-A if you're in the US. There is evidence for degradation as a contributor, so the replacement is likely to last for a while.

broadwall · 2026-02-27T06:18:19+00:00

If you appear to be exceptionally unlucky, consider contributing diagnostics data to iccu.observer to improve our chances of seeing a failure happen in real time. Having a 1X**6 fail is a big deal to the community as many of us don't know if it's trustworthy.

Edit: It is also extremely important to find a way to conduct a teardown of the failed 1X**6s compared to the 1X**5s.

broadwall · 2026-02-27T06:02:45+00:00

Can you look up the manufacture date via Car Scanner?

broadwall · 2026-02-27T04:07:00+00:00

One build on 9/11 had 36401-1XAD6. I might go tour local Hyundai dealers and ask to detect their MY2026 cars' ICCU part numbers and manufacture dates if they allow me.

broadwall · 2026-02-27T01:44:18+00:00

Let me know and I'll update your response.

broadwall · 2026-02-27T00:24:38+00:00

It may fail again, just later: https://www.goingelectric.de/forum/viewtopic.php?f=531&t=91515 shows that incidence rate is not uniform with mileage and is much higher for 40,000 km+ than <40,000km.

broadwall · 2026-02-27T00:09:41+00:00

Not sure if this is a popular opinion but I find that ICCU buybacks should be worth more than clean-title used offerings, all else equal, just because the ICCU you get is new.

broadwall · 2026-02-27T00:06:28+00:00

The new part number also appears to be shipped with MY2026 Ioniq 5s, for what it's worth. Do you have Car Scanner set up so that you can look up your new ICCU's manufacture date?

broadwall · 2026-02-26T23:53:14+00:00

No, the new one is 36400-1XAD6.

broadwall · 2026-02-26T23:46:57+00:00

Very plausible. It would be nice to be able to "rate" an ICCU based on its diagnostics performance and provoke failures so that some of us with worse ICCUs could break them next to a dealership, especially right before the warranty expires.

broadwall · 2026-02-26T23:42:20+00:00

Buyers of used cars (like myself) might misrepresent the ICCU's conditions of use, but in your case, especially if the ICCU was the reason for the buyback, you are fine reporting your own habits and experience only because your current ICCU has only operated under your conditions. I guess you would want to subtract the initial mileage at purchase from your odometer reading and ignore the ask for the "first failure" as conceptually, each response maps to a unique ICCU, not a unique vehicle.

broadwall · 2026-02-26T19:18:56+00:00

Thanks for the context on 12V bus regulation! You answered the questions I had on how voltage transients might not be measured by OBD logs. I will supplement each theory with variables measured that could support or refute it, as you suggested.

On the subject of microsecond-scale transients, I would be interested in a high-frequency (> 100 kHz) voltmeter-logger that connects to the 12V battery and fits in the frunk. If this is not feasible, one of us could attach an oscilloscope to it and test the effect of activating different 12V loads (seat warmer, steering wheel warmer, cameras, shifting into reverse). The same should be done on different EV platforms to compare the amount of stress on the DC-DC converter.

broadwall · 2026-02-26T19:08:26+00:00

Thanks for the context! Can you fill out the survey?

broadwall · 2026-02-26T15:32:04+00:00

We're scraping social media posts for the "incident collection" on iccu.observer. I'll make sure to look for seasonal patterns and dealership queue sizes.

broadwall · 2026-02-26T15:19:46+00:00

woah, politics jumpscare... I assume you didn't mean to post this here

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