DETROIT >> In September, Hyundai and Kia issued a recall of 3.4 million of its vehicles in the United States with an ominous warning: The vehicles should be parked outdoors and away from buildings because they risked catching fire, whether the engines were on or off.

Six months later, most of those autos remain on the road — unrepaired — putting their owners, their families and potentially other people in danger of fires that could spread to garages, houses or other vehicles.

Hyundai and Kia have acknowledged that there’s little hope of repairing most of the affected vehicles until June or later, roughly nine months after they announced the recalls. (Hyundai owns part of Kia, though the two companies operate independently.)

The two companies attributed the delays, in part, to the huge number of vehicles involved, among the largest recalls they’ve ever done. The fires, they say, have occurred when brake fluid leaked onto the circuit boards of antilock braking systems, triggering an electrical short and igniting the fluid.

The companies say they’ve been unable to obtain enough of the needed parts — fuses that reduce the boards’ electrical currents — to fix most of the affected vehicles. Among them are some of their top-selling models for the 2010 through 2017 years, including Hyundai’s Santa Fe and Elantra and Kia’s Sportage and Forte.

Hyundai and Kia have urged the vehicles’ owners to contact the companies or dealers if they see dashboard warning lights or smell something burning. In the meantime, both companies contend that despite the ongoing risks, the cars remain safe to drive.

When they announced the recalls in September, the two automakers reported that the defect had caused 56 vehicle fires and “thermal incidents,” which include burning, melting and smoking. No injuries or deaths have been reported, either before or since the recalls were announced.

Safety advocates complain, though, that the repairs are taking far longer than fixes from auto recalls normally do. Typically, such repairs begin in 10 weeks or less, though some can take longer if automakers cannot quickly determine the cause, which isn’t the case with the Hyundai-Kia problem.

While awaiting repairs, owners of the affected vehicles need to park outside and away from other vehicles to minimize the risks. In the meantime, safety advocates note that if too much brake fluid leaks, it could impair braking or lengthen the distance required to stop a car.

The long-delayed repairs mark the latest in a long series of recalls involving engine fires on Hyundai and Kia vehicles that have bedeviled the two Korean automakers since 2015. All told, 13 million of their vehicles have been recalled for engine problems since 2010.

With the current recall, auto safety advocates say they’re mystified about why it’s taking so long for Hyundai and Kia to obtain the necessary fuses, a relatively simple part. Some also question whether a fuse will reliably solve the brake fluid leak. Some critics say the companies may be trying to save money by identifying the solution as a new fuse, which is far less expensive than fixing the fluid leaks.

“They’re putting a Band-Aid on this thing,” said Michael Brooks, executive director of the nonprofit Center for Auto Safety. “It looks like it’s a cheap fix instead of repairing the entire antilock brake system.”

Advocates say they wonder, too, why regulators at the National Highway Traffic Safety Administration haven’t forced the companies to repair the leaks.

A NHTSA spokeswoman said the agency is monitoring the effectiveness of the recalls and “is working with the automakers to ensure the highest level of safety.”

Hyundai has said that repairing the affected vehicles requires an intricate fuse assembly, with new covers and labels. Although just one fuse will be added to each vehicle, both automakers said they must obtain multiple types of new fuses to cover all models.

“To expedite the remedy,” Hyundai said in a statement, “we are working closely with multiple suppliers, emphasizing the high priority of the recall, and ensuring quality for the replacement fuses.”

A schedule that Hyundai filed with the government shows that owners won’t start receiving letters advising them to take their cars in for repairs until April 22 at the earliest. Most of them won’t get the letters until May or June — eight or nine months after the recalls were announced. Some owners of the affected Kia vehicles might not be notified until the end of June, documents say.

In a statement, Kia said the new fuses it’s seeking were developed to prevent fires, “regardless of what the cause of the electrical short circuit condition may be.” It said it’s working with parts suppliers to accelerate production of the fuses.

Both companies said that besides adding a new fuse, dealers will fix any brake fluid leaks that might be found during inspections. Brake fluid can leak if O-rings, which seal the fluid, lose strength if exposed to moisture, dirt or other contaminants in the fluid, according to Hyundai documents filed with NHTSA. If the fluid level drops significantly, Hyundai said, the driver would see a warning light.

Since September, more than 500 owners have filed complaints accusing the automakers of taking an unreasonable amount of time to make repairs, a review of NHTSA records shows. The Hyundai and Kia fires have continued to occur while owners await repairs; at least five complainants have reported engine compartment fires.

Several complainants said they fear driving the vehicles and want NHTSA to force the companies to provide loaner cars or at least speed up the pace of repairs. Hyundai told dealers last year that they should provide loaners — at Hyundai’s expense — for owners who don’t feel safe driving their vehicles. After an inquiry from a reporter, Kia said it, too, would provide loaners.

Some complainants say they were confused by Hyundai statements saying the recalled vehicles can be driven even though they can catch fire while the engines are running.

“This safety recall sounds urgent and incredibly dangerous,” an owner of a 2012 Hyundai Accent from Burbank, California, wrote in a complaint to NHTSA in December. (People who file complaints aren’t identified in the NHTSA database.) The owner couldn’t understand why Hyundai would say the Accent is safe to drive yet admit that it can still catch fire while being driven.

Both companies said that while fires remain rare, if they do happen, owners would smell smoke or see warning lights on the dashboard. The warnings would “allow for a safe exit from the vehicle,” Kia’s statement said.

But Brooks of the Center for Auto Safety argues that it’s irresponsible for the companies to assure owners that the vehicles are safe to drive when they know fires are possible. If smoke or warning lights should appear, he said, the companies can’t predict how long the occupants would have to escape or free children or other passengers who might be unable to get out on their own.

“There are a lot of (fire) situations where consumers simply weren’t aware,” Brooks said. “That is going to compromise the time they have to escape the vehicle if there’s a fire.” He urged every owner of a recalled vehicle to seek a loaner car from the companies.

Another complainant, from Austin, Texas, called on NHTSA to force Hyundai to fix the fluid leaks.

“They do not appear to be fixing the root cause of the issue,” wrote the complainant, the owner of a 2013 Hyundai Tucson. “Leaking brake systems are a safety concern of the highest magnitude, right up there with tires and steering. This is just insane.”

Ellen Maisano of Gouldsboro, Pennsylvania, said she parked her 2011 Kia Soul in her yard for four months until trading it in last January out of frustration with the slow repairs.

“I don’t want to be on the highway and catch on fire,” said Maisano, who also complained to NHTSA, which, in turn, referred her to Kia.

Nor did she want to leave the Soul near other vehicles in her workplace parking lot. And she worried about parking it in her garage.

“All I need is the garage to go up in flames,” she said.

Maisano and her partner had to share his car to commute to work, which became difficult after four months. Neither Kia nor her dealership nor her insurance company, she said, would pay for a rental car. So she decided to pony up $23,000 for a used Honda HR-V, with a monthly payment of $410 that she hadn’t wanted to spend.

Like some other owners, Maisano said she also worried, in light of an epidemic of Hyundai and Kia thefts, about her Kia being stolen when left outdoors. Many of the vehicles being recalled for potential fires also are at risk of being stolen if parked outside because they lack computer chips in the keys and ignitions that must match up before the engines can be started.

Thieves were able to easily steal the cars with a screwdriver and a USB cable, a method that was shared on videos on TikTok and other social media sites. To try to stop the thefts, Hyundai and Kia issued software updates in February 2023 and offered free steering wheel locks.

Documents that Hyundai and Kia filed with regulators show that the companies have traced the fire problem to brake control units made by Mando, a South Korean supplier. In October, after the Hyundai and Kia recalls, Mando issued its own recall, for 3.4 million anti-lock brake modules that can leak fluid.

Some of those modules also went to General Motors, which said it positions them differently from Hyundai and Kia. GM said it doesn’t know of any incidents involving the modules, and an internal investigation determined that there was no risk to customers.

Mando did not return messages seeking comment.

In November, NHTSA began investigating whether Hyundai and Kia should have acted faster to recall vehicles with Mando control units that could catch fire. Since 2016, each automaker has announced eight recalls, covering about 6.4 million vehicles with the brake units.

NHTSA documents show 92 fires attributed to vehicles in the 16 recalls, including the ones announced in September. In 2020, NHTSA forced both automakers to pay $137 million in fines and for safety improvements for being too slow to recall vehicles with engine problems.

Sean Kane, president of Safety Research & Strategies, which conducts research for lawyers that sue automakers, said that while he welcomes NHTSA’s investigation, the agency should have required more recalls and repairs sooner.

“It’s remarkable that it’s gone on as long as it has without much scrutiny,” Kane said. “I don’t think this problem is over yet in terms of the recall situation.”