The US auto safety authorities have closed a probe into engine fire risks on Hyundai Motor and Kia vehicles as the South Korean automakers’ recalls have lowered fire rates, according to Reuters Thursday.

The National Highway Traffic Safety Administration said the majority of the recalled Hyundai and Kia cars reported lower fire accidents after they underwent the necessary fixes whereas those that had not been repaired showed relatively high fire rates.

The US safety authorities first began the investigation in 2019 and leveled up the probe in 2021 as they recognized 161 fire incidents from engine malfunctions.

Hyundai and Kia conducted eight recalls, bringing in over 3 million vehicles to cope with the engine issue throughout the investigation period.

The Korean carmakers earlier told the US authorities that they will send reminders to the car owners of affected engines every eight months for the next three years to complete the recall process.

The NHTSA said the automakers have been installing engine control software that can send warnings to the driver by sensing potential engine problems and limiting the engine’s output. The companies decided to extend engine warranties.

The American offices of Hyundai and Kia in September issued “park outside” recalls for the owners of the impacted vehicles, notifying them to park their cars outside and away from homes and other structures until the cars have been repaired. According to the companies, fires could happen whether the car is parked and turned off or the engine is running.

The automakers said the vehicle’s anti-lock brake system module could leak brake fluid and result in an electrical short, which could cause significant overcurrent in the module and increase the risk of an engine fire.

The US authorities in November began another investigation into 16 recalls issued by Hyundai and Kia over brake fluid leaks, which could potentially end up as fire accidents. The automakers have recalled some 6.4 million vehicles since 2016.

Meanwhile, Hyundai and Kia posted a record year in 2023 as they sold 1.65 million vehicles in the US market last year. The previous highest figure was 1.49 million set in 2021. Together, they took the fourth largest auto manufacturer rank in the US behind General Motors, Toyota and Ford, outpacing Stellantis for the first time.