The Oct. 20 announcement knocked Tesla stock down more than 6 percent and cast doubt on Tesla's ability to deliver reliable cars in large numbers.
"It's one thing to have a quirky, problematic car that sells 20,000 units per year to wealthy people who probably own at least one backup vehicle," the magazine wrote. "It's quite another when Tesla scales up [to mass-market customers] who may not have the luxury of being so forgiving."
CEO Elon Musk has often described Tesla as a Silicon Valley software company that just happens to make cars. "We really designed the Model S to be a very sophisticated computer on wheels," he said during a press event this March.
When it comes to software, Tesla has superior capabilities. This month Tesla used an over-the-air software update to release a feature called Autopilot, which allows its vehicles to pilot themselves through traffic jams and park themselves along a curb.
Such updates "allow Tesla to diagnose and fix most bugs without the need to come in for service," Tesla said in a statement last week, noting that many problems cited by Consumer Reports have been fixed on the assembly line.
"In instances when hardware needs to be fixed, we strive to make it painless."
So far, Tesla has weathered its quality glitches. Its early-adopter customers, enthralled with the technology in the Model S, have accepted the car warts and all.
Tesla has cultivated that following with a factory-owned service network that bends over backward for customers, many of whom are still covered by Tesla's 4-year/ 50,000-mile warranty, plus the 8-year/unlimited-mileage warranty for the batteries and powertrain. So when Consumer Reports polled Tesla owners on their service experience, 97 percent said they would buy a Tesla again.
For Tesla, which is now developing the mass-market Model 3 for a launch in late 2017, improving on the quality and reliability of the Model S will be a crucial test.
"People don't quite appreciate how hard it is to manufacture something," Musk told analysts last fall. "It is really hard. I have great respect for people who manufacture large numbers of complex objects."