ICCU: The Four-Letter Word Hyundai Ioniq Owners *Hate*
OK, technically it’s an acronym. But for certain unfortunate Ioniq owners, it’s also the sum of all fears.
Our long-term 2024 Hyundai Ioniq 6 has been delightful and utterly reliable so far, nearly 6,000 miles into our time with it. But for a small and extremely frustrated contingent of Ioniq 6 owners or lessees, their ownership experience has been a disaster.
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Imagine this: You’re driving along in your Hyundai Ioniq 6 (or any other Hyundai/Kia/Genesis vehicle built on the E-GMP electric vehicle platformon sale today), and suddenly all hell breaks loose. The dash lights up with a warning about the vehicle electrical system. A “Power Limited” warning appears, with an adorable turtle icon—an improbable harbinger of a serious issue. Soon, the accelerator pedal doesn’t respond to the commands your foot is sending it. The car slows to a halt. Something is very, very wrong: the feared Integrated Charging Control Unit (ICCU) failure.
While this hasn’t happened to our red electric sedan, for Ioniq 6 owners who have been affected it often entails a lengthy stay at a dealership so the parts can arrive, and, more frustratingly, it sometimes occurs after fixes owners thought would prevent the problem in the first place.
What Is an ICCU?
First, some background. Like all contemporary electric vehicles, there are actually two batteries onboard our Ioniq 6. One is the large traction battery, used to move the vehicle around. It’s usually lithium-ion or lithium iron phosphate (LFP), and it’s the big one you generally think about when you think about EV batteries. There’s also a very ordinary 12-volt battery onboard, just like in internal combustion cars. In an internal combustion car, the 12-volt battery is used to start the car and to buffer electricity from the alternator to power the vehicle’s 12-volt systems, like the radio and lights. The alternator that charges this battery is powered by a belt driven off the engine.
In some ways, the 12-volt battery in an EV is like the one in an internal combustion vehicle. While the electric motors need a large amount of electricity to function, like the 800-volt architecture of our Ioniq 6, there are a lot of other systems that don’t—and shouldn’t. Consider the vehicle’s computer and the relays it controls. Those are powered by the 12-volt system, and then they command the large, high-voltage traction battery to power on and energize the motors. When the car’s not in use, the ECU closes the power relays, and the high-voltage traction battery essentially shuts down and disconnects. That means to start the car, you need to wake up the computer. And to wake up the computer, you need 12-volt power. Since EVs don’t have engines, there’s no alternator to keep the 12-volt battery topped up. The E-GMP vehicles use the ICCU to control charging for both the 12-volt and the traction batteries.
To understand why that’s a nifty trick for a single piece of equipment, here’s how Hyundai itself describes the purpose of the ICCU: “Unlike previous BEVs, which only accept one-way charging, the E-GMP’s charging system is more flexible. The E-GMP’s newly developed Integrated Charging Control Unit (ICCU) represents an upgrade from existing On-Board Chargers (OBC), which typically only allow electricity to flow in a single direction from an external power source. The ICCU enables a new vehicle-to-load (V2L) function, which can additionally discharge energy from the vehicle battery without additional components. This enables a BEV based on the E-GMP to operate other electric machinery (110 / 220V) anywhere. The system can even be used to charge another EV.”
The novelty here is that the ICCU can send power where needed, without needing a separate charging or V2L system on top of the OBC. Even when the car isn’t plugged into a charger, the vehicle monitors the state of charge of the 12-volt battery and can send some power from the traction battery to the 12-volt through the ICCU. But the vehicle needs a minimum amount of 12-volt power to do this, since it still needs the 12-volt battery to wake up the computer, which tells the ICCU to divert traction battery charge to the 12-volt battery.
Sounds great on paper. It does what it says: controls the flow of power into and out of both onboard batteries. So, what’s the problem?
The Trouble With ICCUs
The problem is twofold: the ICCU failures themselves, and Hyundai’s response to the issues. Let’s start with the former. What we know for sure is that the ICCU can sometimes fail. There are reports of the coolant that circulates inside the ICCU module leaking due to a manufacturing defect, causing a failure inside the ICCU that prevents the 12-volt battery from charging—at least in South Korea. The official NHTSA recall documentation indicates that the problem results from the failure of the MOSFET (a transistor) that results in an open fuse, which prevents 12-volt charging, but there’s no hard information about what causes the MOSFET to fail.
Failure requires replacing the ICCU unit and the fuse, as well as draining and refilling the coolant. A software upgrade is also implemented, which is supposed to reduce the incidence of failure. The 2024 recall, which affects 2022–2024 Ioniq 5s (including my personal Ioniq 5, which just had its recalls done) and 2023–2024 Ioniq 6s, is to update the software and to check the ICCU, which would be replaced if needed. MotorTrend’sKia EV9 also has some technical service bulletins (TSBs) related to the ICCU/VCU issue.
The Frustrating Part
Vehicles are complex, the ICCU is a new sort of integrated charging system, only a small number of E-GMP cars are so-far affected by the ICCU, and recalls happen all the time. What’s the big deal?
Well, there are several frustrations with how the ICCU issue has unfolded, as a cursory search will reveal the countless threads on Ioniq forums and Reddit of frustrated owners dealing with ICCU failures, long waits for parts, and multiple recalls and updates.
For one, the failure itself is dramatic. The car loses power, immobilizing it. Forget limp-home mode, this is roll to a stop and call a tow truck. Then there’s the wait for diagnosis and repair. At certain points over the course of the ICCU issue, the wait for a replacement ICCU and/or fuse has stretched into months, according to owners’ reports—of which you can find many examples on Reddit subs and enthusiast forums.A few highlights:
“I bought an Ioniq 6 a month back and it has only 850 miles on itand is with the dealer from 1 week. It just completely shut down on me at a traffic signal with electric system failure message. Completely got locked —not going in neutral or doing anything at all. I have to get it towed to the dealership in the middle of the night after Hyundai roadside was not able to secure a tow for me after waiting for five hours. Based on preliminary assessment, it’s the ICCU that they are replacing and will take at least another two weeks. It’s not been the best experience to say the least .... brand new car breaking down within a month of being brought.
“All said, I've had intermittent possession/the use of my EV6 for something like 5 of the 9 months I've owned it, and I'm currently without it once again with no resolution in sight. So, my estimated wait time for EV6 repairs is indefinite-to-infinity. YMMV.”
“Towed it to the dealership and they’re waiting for the fuse and a new ICCU to show up as the parts are in massive backorder, which means approximately two months of waiting. It feels like Hyundai doesn't know where exactly the problem is and they're going into trial-and-error mode till they find the right part to replace.”
So, for some affected owners, the ICCU failure wasn’t just experiencing the car losing power unexpectedly, it ended up being a drawn-out and frustrating process involving several software updates, and long waits—several months, according to some—for new parts. And these frustrated owners made their feelings about the process very clear on social media, forums, and the like. Owners don’t go online and take time to write about a lack of problems with their car, but they will to vent their frustration about a failure that still seems to occur even after several recalls.
The result is that Ioniq intenders going online to research owner experiences find an overrepresentation of ICCU failure horror stories, leading some to wonder if the issue is a dealbreaker.
What Has Hyundai Said About the ICCU Failures?
Officially, not much. We asked Hyundai a myriad of specific questions about why the failures occur but only received a cursory response from a representative, which is as follows:
“All the referenced vehicle concerns have been addressed through several countermeasures already implemented in our newest vehicles and through the issuance of recalls, service campaigns, and several technical service bulletins. These recalls, campaigns, and bulletins assist in the diagnosis and repair of vehicles produced before these countermeasures were implemented. If any customer is experiencing any of these concerns, the best course of action is to schedule an appointment with their nearest Hyundai dealership.”
A Big Deal for Some, but How Many?
The question you’re probably asking is, what’s the risk of this failure with any given E-GMP vehicle? It’s not clear on an individual vehicle basis, but the information we do have indicates that it’s not a significant percentage of vehicles on the road. Hyundai, in its NHTSA recall documentation from 2024, notes that Hyundai’s North American safety office had information that 618 incidents of the failure had occurred from March 2022 to March 2024. The latest recall information indicates that around 1 percent of E-GMP models from the relevant model years are affected (out of 145,235 that could potentially have the defect). That’s roughly 1,420 vehicles, potentially—statistically, not a huge deal.
What Did We Do About It?
At just under 6,000 miles, with a maintenance reminder warning on the instrument cluster, and a recall notice mailing in hand, we decided to make an appointment with our local Hyundai dealer and get the latest software installed on the Ioniq 6, as well as have the ICCU and its fuse inspected. At the same time, we opted to do the recommended multipoint inspection. We weren’t concerned about anything with the car, and the inspection found everything to be fine.
The car ended up getting three separate software updates, instead of just the one we were expecting. The service manager told us one of them was rather lengthy, so it’d be a few hours. Instead of waiting, we hopped on the offered rideshare and headed home.
The first update was for the vehicle control unit’s “limp-home mode.” It’s related to, and part of, the overall ICCU recall. Basically, this one adjusts the maximum vehicle speed as it starts to lose 12-volt battery voltage because of the ICCU failure. The second changes the vehicle charging logic when plugged into a Level 2 (240V) charger. In some cases, E-GMP owners have had trouble with charging slowing down or stopping as the car tries to prevent damage to the charge port and cable. This update allows the vehicle charging management system (VCMS) to restart itself and continue charging. This was another pain point for some owners.
The last update was the latest ICCU software update as part of the recall, and according to NHTSA documents, this does several things. First, it changes the way the ICCU uses the traction battery to recharge the 12-volt battery. The software causes the low-voltage DC-to-DC converter (LDC) to do a “soft start” when it begins to top up the 12-volt battery, which Hyundai says reduces over-voltage at the beginning and end of the charge cycle. It also updates the way in which the radiator fans and water pumps operate, to improve “thermal loading conditions during operation.” We presume that means the cooling system will kick on more often and with more gusto to keep things cooler while the LDC is running.
The Result: A Clean Bill of Health
All software updates went off without a hitch, so we’re now driving around with the latest software that should reduce the impact of potential ICCU failures—or, at least, alert us to the failure earlier, and maybe buy us a little more time to pull over to the side of the road in the unlikely event that our ICCU kicks the bucket. Our ICCU and fuse looked good during the physical inspection part of the recall, as well.
Much ado about nothing, the snarky among you may think. A long description of a defect that won’t impact 99 percent of the Ioniq 6s—or the other E-GMP cars and SUVs—on the road. But the ICCU issue is basically unavoidable anywhere Ioniq owners gather online to discuss their vehicles or get advice about buying one, arguably skewing perceptions about its prevalence. Who’s writing online about how everything’s boring and fine? Well, we are. And it’s partly to point out that there’s always a bias toward people sharing about their dramatic, noteworthy experiences—which an ICCU failure certainly is for some owners—not to mention the sometimes-painful process to fix (or offload) an affected vehicle. It’s a big deal, but not one that individual E-GMP owners are statistically likely to face.
Like a lot of the other staffers here, Alex Kierstein took the hard way to get to car writing. Although he always loved cars, he wasn’t sure a career in automotive media could possibly pan out. So, after an undergraduate degree in English at the University of Washington, he headed to law school. To be clear, it sucked. After a lot of false starts, and with little else to lose, he got a job at Turn 10 Studios supporting the Forza 4 and Forza Horizon 1 launches. The friendships made there led to a job at a major automotive publication in Michigan, and after a few years to MotorTrend. He lives in the Seattle area with a small but scruffy fleet of great vehicles, including a V-8 4Runner and a C5 Corvette, and he also dabbles in scruffy vintage watches and film cameras.
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