Kia is calling in over half a million of its vehicles in the United States for an electrical issue that could disable some of its most critical safety features. That’s a heck of a lot of vehicles for a single recall, but it concerns a very serious issue.

As points out, the recall stems from an investigation launched a few months ago by the National Highway Traffic Safety Administration (NHTSA).

The government investigators looked into a problem which seemed to have kept the airbags and seatbelt pretensioners from working in certain vehicles made by Kia and its sister brand/parent company Hyundai.

This defect has resulted in four fatalities and six injuries so far in six serious crashes in Kia’s and Hyundai’s cars.

Hyundai responded by recalling nearly 580,000 vehicles in two separate campaigns in February and April. Now Kia is recalling another 507,000 vehicles of its own for what appears to be the same issue. Combined, that comes to nearly 1.1 million vehicles in the United States alone, and an undisclosed number in other markets.

The malfunction is caused by an electrical glitch that overloads the control module in the event of a crash. It appears to be a similar issue to the one that prompted Fiat Chrysler to recall 1.4 million vehicles in the US back in 2016.

In this case, the recall covers certain 2010-13 Forte Sedan and Forte Koup models, 2011-13 Optima and 2011-12 Optima Hybrid saloons and Sedona minivans. Unfortunately a fix has yet to be identified, but the manufacturer hopes to have one in place in time to start calling those vehicles in to dealers towards the end of July.

This comes just days after Kia announced the recall of over 100,000 newer Sedonas over a defect with their power sliding doors.