EV Suddenly Lost Power While Driving: Documented Causes (ICCU, Contactor)

Who this affects

Two separate documented causes. Hyundai and Kia: the ICCU (Integrated Charging Control Unit), covering 2022–2024 Ioniq 5 among others, with Ioniq 6 and Kia EV6 in the same family of campaigns. Ford: the high-voltage battery main contactor on 2021–2022 Mustang Mach-E extended-range and GT models.

Models we track that this is documented against: Hyundai Ioniq 5 · Hyundai Ioniq 6 · Kia EV6 · Ford Mustang Mach-E.

The evidence

Hyundai/Kia ICCU: NHTSA's Office of Defects Investigation opened a formal investigation in June 2023 after collecting 42 owner reports describing a loud pop followed by reduced or complete loss of motive power. A subsequent recall covered 145,351 vehicles in the US including the 2022–2024 Ioniq 5. Hyundai reported being aware of 57 ICCU failure incidents between 25 March 2024 and 5 November 2024, with no reported crashes or injuries. Ford Mach-E: recall 23S56 covered 34,762 vehicles over high-voltage battery main contactors that may overheat; NHTSA later opened a recall query covering 64,727 vehicles after receiving 12 consumer complaints about the remedy.

Likely causes

Hyundai/Kia ICCU failure — the unit that charges the 12V battery from the traction pack fails, so the 12V is no longer replenished. Reported causes are overvoltage at the start and end of the 12V charging cycle, and thermal loading during charging or driving. Once the 12V is exhausted the car cannot maintain the HV system and drive is lost.
Ford Mach-E high-voltage battery main contactor overheating — DC fast charging and repeated wide-open-throttle events overheat the contactors, deforming the contact surfaces. A contactor can then fail to close, or weld closed. One that will not close while driving results in loss of motive power.
A flat or failing 12V auxiliary battery on any EV, from an unrelated cause. The 12V runs the control electronics that keep the HV system energised — if it dies, the car stops regardless of how full the traction pack is.

How to tell them apart

A list of possible causes is only useful if you can narrow it down. These are the observations that discriminate — and they are the ones worth bringing to a shop.

Start with the badge and the year. The ICCU campaigns cover Hyundai and Kia platforms; the contactor campaign covers the Ford Mustang Mach-E. They are unrelated faults that happen to present the same way, so the make narrows it immediately.
What came first? ICCU reports characteristically build up: a "Check electrical system" or "Check power supply" warning appears, sometimes for days, before drive is lost. A contactor failure tends to arrive without that electrical-system preamble.
What were you doing? The Mach-E contactor issue is documented as heat-related, following DC fast charging or repeated wide-open-throttle runs. If it failed on a cold start after a gentle week, that pattern does not fit.
Did the car recover after a 12V jump or charge? If it did, the 12V is at least part of the story — but on a Hyundai/Kia that is as likely to be the ICCU failing to replenish the 12V as it is a tired 12V battery. A 12V that goes flat again within days points upstream.
A plain 12V battery failure is the mundane explanation and it is common. It is the one to rule out first precisely because it is cheap, and because a shop that has not ruled it out may reach for far more expensive parts.

✅ Safe to check yourself

These leave the high-voltage system completely alone.

Check your VIN against the manufacturer's recall lookup and the NHTSA recall database first. If your car is under an open recall for this, the remedy is free and you should not be paying a shop to diagnose it.
Note exactly what the dash said. "Check electrical system" or "Check power supply" messages preceded loss of drive in many ICCU reports, and that wording is useful to the shop.
Note whether a loud pop or bang preceded it, and whether the car had recently been DC fast charged or driven hard. Both are documented triggers on the respective platforms.
Have the 12V battery tested. This is a low-voltage, entirely routine test, and a weak 12V is both a cause in its own right and a downstream symptom of ICCU failure.
Write down the date, mileage, temperature and what you were doing. Intermittent faults are frequently dismissed because the owner cannot demonstrate them, and a dated record is what makes the case.

⛔ Qualified technician only

Not a disclaimer — a genuine boundary. Knowing what sits on this side is also how you tell whether a quote is reasonable.

Any inspection, testing or replacement of the ICCU itself — it sits on the high-voltage side.
Any work on the high-voltage battery junction box or its contactors, which is the Mach-E remedy.
Reading manufacturer-proprietary fault codes from the HV control modules, which generally needs the manufacturer's own diagnostic tooling.
These require de-energisation, verified isolation, rated PPE and formal HV qualification. This is not a job to attempt on a driveway.

Typical resolution

Where a recall applies, the manufacturer remedy is free. Hyundai/Kia ICCU repairs have typically involved a software update, inspection of the ICCU and its fuse, and replacement of failed parts and sometimes the 12V battery. The Ford remedy evolved across campaigns from control-module software updates that monitor contactor temperature and resistance, through to dealers replacing the high-voltage battery junction box. Note that reoccurrence after an initial recall repair has been reported by owners in the Hyundai case.

🇵🇭 In the Philippines

The recall numbers above are United States campaigns. A Philippine-market car is not automatically covered by a US VIN lookup, and the local campaign may differ in scope or timing — check with the Philippine distributor as well as the NHTSA database, and ask specifically whether your VIN falls under a local service campaign. Independent shops here are unlikely to have the manufacturer HV diagnostic tooling this needs, so a casa visit is the realistic route even where an independent would normally be cheaper.

What we could not verify

Whether the ICCU remedy is a permanent fix is not settled — reoccurrence is owner-reported rather than something we can cite from a regulator finding. Recall applicability varies by market and VIN; the figures above are US campaigns and do not automatically describe what was done in other countries. We have no sourced Philippine repair pricing for either fault, so no cost figure is given rather than an invented one.

Sources

Whatever the cause turns out to be, the thing that decides a warranty claim is usually evidence — a dated record of when the symptom started, the mileage, and the service history behind it. Intermittent faults get dismissed when an owner cannot demonstrate them. If you keep that record anywhere, keep it somewhere you will still have it in three years. Kotselog is a web app for exactly that: it logs services, mileage and fuel or charging so the history exists when you need it. It does not read fault codes or diagnose anything — that is what the shop and its tooling are for. Open the web app →

Other symptoms

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EV suddenly lost power while driving