DETROIT — U.S. auto companies such as General Motors, Tesla and Ford faltered this year in Consumer Reports’ reliability rankings as readers reported more mechanical trouble and fewer problems with infotainment systems.

The magazine said all U.S.-based brands fell to the bottom half of 29 brands in the rankings. Lexus and Toyota were once again at the top.

Consumer Reports got more than 500,000 responses to the annual survey of its subscribers, and it uses the data from the 2000-2017 model years to predict reliability of 2019 vehicles.

The survey, which was released Wednesday, found that readers are having more trouble with technology designed to increase fuel economy than they are with electronic infotainment systems, which long had been a bugaboo for automakers and vehicle owners.

The mechanical problems with smaller turbocharged engines and transmissions with multiple gears could leave people stranded rather than just frustrated with voice recognition or other technology, said Jake Fisher, director of auto testing at the magazine.

“It’s worse for the consumer, absolutely,” Fisher said. “I would be happy to not be able to pair my phone five times than get stuck on the side of the road once.”

Mazda, Subaru, Kia, Infiniti, Audi, BMW, Mini and Hyundai rounded out the top 10 auto brands. Volvo had the worst reliability followed by Cadillac, Tesla, Ram and GMC.

Tesla dropped six places from last year and ranks 27th. GM’s Buick, normally a top-10 finisher, tumbled 11 spots to No. 19. Ford was the highest-ranked U.S. brand but fell three places to No. 18.

The domestic brands largely were plagued by problems with newly introduced models, Fisher said.

“Traditionally it’s the older models that have the best reliability. As they cycle through the fleet, we’re seeing a drop,” Fisher said.

In the case of Tesla, the Model S luxury car fell from “above average” reliability to “below average” as readers reported trouble with the air suspension and door handles that extend from the body when the driver approaches. The low reliability score cost the Model S its “Recommended Buy” status with the magazine.

Tesla’s Model X SUV remained “much worse than average” due to problems with its falcon-wing doors and touch screen, while the simpler Model 3 mass-market sedan ranked “average” in reliability.

Tesla introduced more complexity into the Model S by offering all-wheel-drive and air suspension standard, Fisher said. The company makes hardware and software changes weekly, raising the risk of problems, he said.

General Motors’ brands were hurt by mechanical problems including transmissions on its newly introduced large crossover SUVs such as the Buick Enclave, Chevrolet Traverse and GMC Acadia. Buick’s Enclave was the most reliable vehicle the brand had until the redesign, and now it’s the worst, dragging down Buick’s score, Fisher said.

Cadillac, he said, pushes the edge on new consumer-pleasing technology, but that causes reliability problems.

Almost the opposite are Toyota and its Lexus luxury brand, which have taken the top two slots for the sixth straight year, Fisher said. Toyota is slow to introduce new technology, only now offering Apple CarPlay when other automakers did it years ago, he said.

“If you’re slow to the market, you’re slow with technology, that’s the way you do get reliability and that’s how Toyota is so consistent,” he said.

Consumer Reports said it didn’t have enough data to rank Alfa Romeo, Fiat, Jaguar, Land Rover, Maserati, Mitsubishi or Smart.

The magazine gives more weight to mechanical and safety issues than minor problems like voice recognition or wind noise.