Tesla CEO and Chairman Elon Musk on Sunday said the electric vehicle maker will soon bring most collision repairs in-house — a promise he first made during the company's annual shareholder meeting in June.

In a series of tweets on Sunday, Musk blamed outside shops for taking too long to complete repairs.

Specifically, Musk wrote: "Tesla is bringing most collision repairs in-house, as outside firms take weeks to months for repairs, driving Tesla owners (and us) crazy."

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He acknowledged that some collision repair shops are able to turn around a Tesla customer's car after an accident rather quickly.

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When Tesla eventually rolls out its own collision repairs service, he said, the goal will be to make each vehicle "better than before accident."

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Musk also suggested that Tesla has an advantage over outside collision repair shops when it comes to timely service. "Outside repair shops are jack of all trades, which means supporting 1000's of makes & models. Tesla collision repair specializes in three," he wrote. "Having all parts in stock & not waiting for insurance approval also make a world of difference."

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Ron Arth, the owner of Oakland, California, repair shop George V. Arth & Son, told CNBC that he's not sure how Tesla could repair vehicles without waiting for insurance approvals, unless it's willing to do work for free or temporarily carry the cost on its books while it works out approvals. "Collision repair shops have to document everything we do, and justify it in order to get paid for the repairs," he said.