The push for greater fuel efficiency and connectivity behind the wheel is driving many car owners to complain about their vehicle's reliability.
Consumer Reports' annual report on auto reliability, released Tuesday, also found that Toyota's Lexus once again earned the crown as the most reliable brand, while the Tesla Model S slipped to "worse than average" predicted reliability, due to a growing array of complaints from those who own the electric car.
Tesla shares slipped 9 percent to near $206 following the report.
"We're seeing all types of issues [with the Model S]," said Jake Fisher, director of auto testing at Consumer Reports. "Some are annoying issues like squeaks in the hatch or rattles and squeaks in the sun roof, but we're also seeing major issues in terms of the charging systems. We're even seeing people who have to have the entire electric motor replaced."
Consumer Reports said it had heard from roughly 1,400 Tesla owners for this year's survey.
The drop in predicted reliability comes less than two months after Consumer Reports gave the latest version of the Model S a perfect score of 100 following a series of tests by the publication's auto team.
"This is the first time it's ducked below average on reliability and that's disappointing because this is a car that performs very well," Fisher said. "But we are seeing problems as they increase the volume and produce more of these cars."
In a statement to Consumer Reports, a Tesla spokesperson said, "Close communication with our customers enables Tesla to receive input, proactively address issues, and quickly fix problems. Model S over-the-air software updates allow Tesla to diagnose and fix most bugs without the need to come in for service. In instances when hardware needs to be fixed, we keep the customer's convenience and satisfaction top of mind."
Overall, the annual report on what bothers people about the cars, trucks and SUVs they have bought within the last three years shows two areas in which new vehicles are struggling.
First, consumers are frustrated with new transmissions that are not running smoothly — or in some cases, not at all. Fisher blamed this trend on automakers' rolling out new transmissions with more gears, in an effort to improve fuel efficiency. However, many consumers are finding they now have transmissions that feel uneven, or worse, do not shift gears.
"We're seeing issues where these cars don't shift at all. They actually don't have power and you can't drive the vehicle," Fisher said. "Sometimes they have to replace the transmission on brand new vehicles and that's a problem."
Vehicle owners also cited continued frustration with their in-car connectivity systems.
As for the top brands in Consumer Reports' survey of more than 740,000 vehicles owned by its subscribers, Lexus solidified its rank as the most reliable. Fisher said Toyota's luxury brand has benefited from simplifying its in-car infotainment system, and focusing on improving overall quality.
"They [Lexus] are the conservative automaker," Fisher said. "They're not the ones coming out first with new technology. Instead you see cars that gradually evolve."
Meanwhile, Fiat Chrysler continued to struggle with reliability. The Fiat brand ranked last among the 28 brands listed in the survey, coming in right behind its popular Jeep nameplate.
"They're really struggling to keep their quality, and if they don't do something to turn that around they're gonna turn off customers going forward," Fisher said.
Matt Liddane, vice president of quality at FCA North America, said, "We greatly value customer feedback and use it to continuously improve our vehicles. Because of this fact, we're significantly accelerating our pace of improvement for our entire product lineup."
Below are the complete rankings from Consumer Reports. Because the group only tests one Tesla model, it is not included in the list.
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