"Given the number of bits and pieces Tesla has replaced on our car, it might be tempting to guess that its reliability score will go down," the magazine said. "The reality is, it might — depending on the frequency and severity of problems reported by our subscribers and whether they show that reliability is below average."
Rave reviews for Model S, priced from $71,000 in the U.S., by Consumer Reports and Motor Trend, have helped spur demand for the car since the first units were delivered in 2012. Elon Musk, chief executive officer and co-founder of Tesla, said last month that early units of the battery-powered sedan had production flaws.
"We definitely had some quality issues in the beginning for the early serial number cars, because we were just basically figuring out how to make the Model S," Musk told analysts on a July 31 conference call. "I think we've addressed almost all of those for current production cars."
Consumer Reports in February said that Model S was the first U.S. car to receive its "best overall" pick among vehicles tested.
"We are particularly attentive in addressing potential issues, even if those issues appear to be very minor or have a low likelihood of causing any future problems," Liz Jarvis- Shean, a Tesla spokeswoman, said in response to the update by Consumer Reports. "Like any owner, Consumer Reports benefits from the peace of mind afforded by the comprehensive Tesla warranty."
The issues highlighted by Consumer Reports follow a report by Edmunds.com, an automotive data and pricing company in Santa Monica, Calif. It reported problems last month with its Model S that included replacing the main battery pack after incidents in which the car stalled; a frozen touchscreen; a creaky steering wheel and difficulties opening the car's sunroof.
Both Consumer Reports and Edmunds.com said the glitches they experienced were repaired by Tesla and covered under warranty at no additional cost.
Musk has said Tesla continues to review customer reports to ensure all known flaws with the car are fixed.
"Every week I have a product excellence meeting which is a cross-functional group, so we've got engineering, service and production and we go over all the issues that customers are reporting with the car and the action items that have to be addressed to get the car ultimately to the platonic ideal of the perfect car," he said on the call in July.
"That's what we're aiming for, because although I think we've got great service, the best service is no service."
Tesla shares have risen 72 percent this year.