In about 1 in 4 major recalls during recent years, less than half of the vehicles have been fixed within 18 months, the data show. On average, major auto makers have repaired about two-thirds of recalled vehicles by the 18-month mark, according to reports filed with regulators since early 2015.
The uncompleted recalls pose a risk to drivers, who could be injured or killed if the faulty part malfunctions and causes an accident. The Consumer Federation of America estimates there are more than 70 million vehicles on the road today with open recalls that have yet to be repaired.
Ford Motor Co.'s recall of 1.5 million cars last week was just the latest in this year's rising tally of recalls by auto makers. While the number of recalled vehicles dropped last year, it had been on the rise for several years before and hit an all-time high of more than 50 million in 2016, data show.
Mazda Motor Corp. had the lowest average completion rate, at 38% during that period. That low rate is partially attributable to one large recall of older cars. Tesla Inc. and Volvo Cars, with just a handful of small recalls each, had the highest rates, at more than 95%.
The reasons vary, such as lack of parts or the inability for car makers to reach owners, say auto makers and safety experts. They add that while auto makers must notify consumers of recalls via mail, motivating them to respond can be challenging, as many car owners disregard the notices or don't feel urgency to repair their vehicle.
Some car makers, such as Honda Motor Co., have stepped up their efforts in the wake of large-scale recalls, including replacing millions of Takata Corp.'s defective air bags world-wide.
Auto makers are required to submit completion reports to federal regulators for six quarters after a recall begins. Manufacturers typically don't have to continue documenting their progress beyond that even if completion rates are low, though the National Highway Traffic Safety Administration can require extra reports.
The Journal calculated auto makers' recall-completion rates based on their sixth recall status report. To calculate average fix rates, the Journal weighted the findings by the number of automobiles involved in each recall, a method NHTSA has previously used.
Large recalls typically have worse completion rates than small ones, NHTSA research has shown.
Lawmakers and safety advocates have long pressed for more transparency and better enforcement of recall completion, saying that owners are at risk and car makers should try harder to reach people with vehicles in need of repair.
"Recall completion rates are surprisingly lower than one would imagine they would be" given that cars are critical to most Americans' day-to-day lives, said Jason Levine, executive director of the Center for Auto Safety, an advocacy group started in 1970 by Ralph Nader and Consumers Union.
A NHTSA spokeswoman said the agency is committed to working with auto makers and consumers to improve recall rates and is taking steps to raise consumer awareness "on the importance of acting quickly on open recalls."
Ford's latest large-scale recall involved a part that can malfunction and cause the fuel gauge to register improperly. The defect could cause stalls and crashes, the company said.
Ford's overall fix rate is in line with the national average. The company's 2016 recall of faulty Takata air bags in more than 300,000 pickup trucks was the slowest in the Journal's analysis of more than 200 recalls affecting at least 100,000 vehicles. The company fixed about 0.2% of Takata air bags within 18 months after the recall began.
The recall's completion rate was low because it offered an interim fix that would require a follow-up, a Ford spokeswoman said. She said the company conducted a separate recall campaign once a permanent fix became available, and it closed the first recall.
The second recall didn't begin until about 22 months after the interim fix was announced, federal data show. A Ford spokeswoman said the delays were caused by the challenge of redesigning a part for a recall of this size and complexity and production constraints. Based on the first three quarterly reports, it has a completion rate of 28%. Ford said the completion rate has risen to 33% since the latest report was filed on July 30, and the company is reaching out to customers via phone calls, text messages and emails.
Nationwide, completion rates have dipped in recent years, the data show, but they have rebounded this year to about two-thirds. Recalls by major auto makers that hit the 18-month-mark last year had an average completion rate of about 60%, down from 69% two years earlier.
Recent low completion rates reflect the sluggish pace of many Takata air-bag recalls, which had parts shortages. Takata-related fixes made up four of the 10 slowest recalls in the Journal's analysis of large recalls.
Auto makers also vary in how fast they are at finishing recalls, though it isn't possible to determine whether that is due to the efforts of the manufacturer or other factors, such as the type of cars involved.
Mazda's low completion rate stems in part from one especially large, slow recall. The company recalled more than one million ignition switches prone to catching fire in 2015. Eighteen months later, less than 1% were fixed.
A Mazda spokeswoman said the low completion rate for that recall is likely due to the age of the vehicles. The model years affected by the recall ranged from 1989 through 1998.
"While we suspect that many of the vehicles in the recall are no longer on the road, we are still working to increase the recall completion rates," the Mazda spokeswoman said.
It is harder for auto makers to find the current owner in older cars that go through multiple owners, according to the Alliance of Automobile Manufacturers, a trade organization. Older vehicles also have a higher chance of being taken off the road either because of poor performance or damage, making the fix no longer necessary, the group said.