(Reuters) - Consumer Reports said Tuesday it will retest brakes on Tesla Inc’s new Model 3 sedans after Chief Executive Elon Musk promised a software update, but the potential hit to sales from the magazine’s negative review weighed on Tesla shares.

A review by the influential magazine on Monday said the car, despite many positives, had “big flaws,” including braking slower than a full-sized pickup truck. That criticism adds to headaches for Musk, already facing pressure over a series of crashes, production issues, and the company’s finances.

“If Tesla can update the brakes over the air - an industry first - we’d be happy to retest our Model 3,” said Jake Fisher, Consumer Reports’ director of automotive testing.

In mass-market, mid-sized cars, vehicles recommended by Consumer Reports account for over 80 percent of the category’s sales volume, Barclays analyst Brian Johnson wrote in a client note.

Musk in a tweet late on Monday acknowledged the brake issue and said that the magazine’s tests had used two early versions of the car before improvements had been made.

“Looks like this can be fixed with a firmware update,” Musk tweeted, saying Tesla aimed to roll out a solution a few days. “With further refinement, we can improve braking distance beyond initial specs.”

Musk said he would ask Consumer Reports to retest using a more recently built car.

The Silicon Valley company uses so-called “over-the-air updates” (OTAs) to send software fixes and improvements to its cars.

FILE PHOTO: A man cleans a Tesla Model 3 car during a media preview at the Auto China 2018 motor show in Beijing, China April 25, 2018. REUTERS/Jason Lee/File Photo

Tesla stock, down more than $100 a share since September, fell 3.3 percent to $275.01 on Tuesday. The shares

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