This is as good as it gets for auto buyers and owners, according to Consumer Reports magazine.

The best brands have stopped getting better and so have the others, the magazine's data for the past five years show. "It could indicate that the most-reliable new cars have reached a practical limit as to how trouble-free they can become," according to the magazine's annual April auto issue, on newsstands Monday.

"We've reached a difficult level to break," says Anne Stevens, chief operating officer of Ford Motor's North and South American operations. "That doesn't mean don't keep trying."

The magazine is thought to sway hundreds of thousands of auto-buying decisions annually. "It's very influential, no question," says Jim Hossack, consultant at AutoPacific, a research and consulting company. "In consumer focus groups, when you ask what influences them, Consumer Reports comes up frequently."

David Champion, head of auto testing for the magazine, says the quality plateau probably is due to increasing use of electronics in cars.

"The electrical and electronic features tend to be problematic, so they could be causing a leveling off of reliability even though the rest of the car is getting more reliable," he says.

That also could help explain the higher scores of Japanese models. "The Japanese economy has been built on consumer electronics ... so they might have an advantage in that the supplier structure is more used to working with electronics and is better at it," Champion says.

Hossack suggests that the cost-benefit ratio might have maxed out, and improving much more "would cost the manufacturer more than it's worth. It might not be a technical issue, but a practical, economic limit."

The best appears to be an average of 12 problems per 100 new vehicles. That has been the average of all the Asian brands since improving from 15 per 100 in 2002.

Detroit brands have been stuck at about 17 or 18 problems per 100, while European makes, which typically are the most expensive, are holding at 20 or 21 problems per 100 vehicles the past few years, Consumer Reports data show.

Those numbers are based on yearly surveys of the magazine's readers. The latest survey covered a record 1 million vehicles of all brands and types.