Every domestic automaker landed in the bottom half of the magazine's new-car reliability rankings, which include data collected for more than 500,000 vehicles. The survey, which ranked 29 brands in the U.S. market, was released on Wednesday.
"It's the complexities that have really dragged down Tesla," said Jake Fisher, the magazine's director of auto testing. "The majority of the problems that we're seeing with Tesla truly are mechanical issues."
The Model S appears similar to the model launched six years ago, but Tesla has made significant mechanical and software changes over the past few years, including making air suspension and all-wheel-drive standard, he said. That can hurt reliability as more complexity is added.
Tesla said it had streamlined and simplified Model S configurations, not made them more complex. It also said the issues cited by owners in the Consumer Reports survey had previously been addressed by the carmaker, including with over-the-air software updates.
"Not only are our cars the safest and best performing vehicles available today, but we take feedback from our customers very seriously and quickly implement improvements," the company said in a statement.
Tesla said that was why the Model S has been top ranked on Consumer Reports' owner satisfaction survey every year since 2013, when the carmaker was first included.
Toyota Motor Corp's Lexus and Toyota brands took the top two spots in the survey, as they have for six consecutive years. The survey results can be found at CR.org/reliability.
The magazine's annual survey of new vehicle reliability predicts which cars will give owners fewer or more problems than their competitors, based on data collected. Its scorecard is influential among consumers and industry executives.
Tesla's ranking slid to No. 27, ahead of only General Motors Co's Cadillac brand and Volvo.
The Model S, which starts at $74,500, dropped to "Below Average" from "Above Average" last year, and its overall score denied it Consumer Reports' "Recommended" tag. Owners reported suspension problems and other issues, including problems with the extending door handle, the magazine said.
Tesla's Model X SUV remained "Much Worse Than Average" with ongoing problems, including with the falcon-wing doors and center display screen. The Model 3 sedan, seen as key to Tesla's profitability, debuted with "Average" reliability.
In May, Consumer Reports recommended the Model 3 after its latest tests showed a software update improved the car's braking. It has maintained that rating.
Tesla was scheduled to report third-quarter results after the market close on Wednesday.
Other domestic brand rankings included: Ford Motor Co's Ford and Lincoln brands at No. 18 and 20; GM's Buick, Chevrolet and GMC brands at No. 19, 23 and 25; and Fiat Chrysler Automobiles' Dodge, Jeep, Chrysler and Ram brands at No. 21, 22, 24 and 26, respectively.
Rounding out the survey's top five were Japan's Mazda Motor Corp, which registered the biggest gain, by nine spots; Subaru and Hyundai Motor Co's Kia brand.
