Ford Motor Co. suffered a big drop in auto quality this year, mainly due to a complicated entertainment system in its cars, while Toyota Motor Corp.'s Lexus rebounded from a poor showing last year, according to a closely watched industry study.

Lexus was once again the top-ranked car in overall quality, according to J.D. Power and Associates, which released its initial quality study on 2011-model year vehicles on Thursday. The annual ranking is based on surveys of thousands of new-car buyers and tracks the complaints they find in their first 90 days of ownership, reported The Wall Street Journal.

Honda Motor Co. placed second, followed by Honda's Acura brand and Daimler AG's Mercedes-Benz. General Motors Co.'s Cadillac and GMC brands improved and scored above the industry average. Chrysler Group LLC's Chrysler brand and GM's Chevrolet also improved from 2010 but were still below average. Chrysler's Jeep was near the bottom and its Dodge brand was last.

The biggest surprise was the decline in the scores of Ford and Hyundai Motor Co., two companies that had climbed to near the top of the industry in quality in recent years.

In this year's survey, Ford was knocked down to 23rd place and well below the industry's average for complaints; a year ago it was ranked fifth in quality.

Ford's problems seem isolated to the introduction of the MyFord Touch system, which uses a touch-screen interface to operate the entertainment and phone system, the research firm said.

"They've had some challenges with the [MyFord Touch] technology early on," said Dave Sargent, a senior analyst with J.D. Power.

Ford has acknowledged that the system has quirks that need to be ironed out. "We expected mixed quality results this year," Ford Executive Vice President Mark Fields said in a statement. He added that customers now tell it "we largely are back on track after addressing near-term quality issues with MyFord Touch and a few of our powertrains."

Hyundai was hurt because it had two popular cars, the Sonata sedan and Elantra compact, that were new to the market, Mr. Sargent said. New vehicles in their first year on sale tend to have more defects.

In general, vehicles that were redesigned or were all-new for 2011 had worse scores than a year ago, according to the study. J. D. Power found 122 complaints for 100 redesigned vehicles covered by the survey, up from 111 in 2010. There were only 103 problems reported for every 100 vehicles that were largely unchanged from 2010, an improvement from 108 a year ago.

Lexus had the best score, with just 73 problems found in every 100 cars sold. The Japanese luxury brand had the best scores in the J.D. Power survey for several years in a row, but fell back last year amid its parent company's troubles with unintended-acceleration complaints.

Honda had 86 problems, Acura 89 and Mercedes 94. The top 10 was rounded out by Mazda, Porsche, Toyota, Nissan Motor Co.'s Infiniti brand, Cadillac and GMC. All were above the industry average of 107 problems for every 100 vehicles sold.

The Toyota brand moved all the way up to seventh place after plunging to 21st last year. The survey's results for Toyota last year were gathered during the height of its recall crisis for unintended acceleration and may have affected consumer attitudes, Mr. Sargent said.

Hyundai had 108 complaints for each 100 vehicles sold, one fewer than the industry average of 107.

Ford had 116 problems for each 100 vehicles.