Tesla engineers were quietly concerned with Elon Musk's early claims about the company's self-driving tech, according to a new book

• Some early critics of Elon Musk's self-driving claims were Tesla engineers, a new book says.
• The reporting comes from "Power Play: Tesla, Elon Musk, and the Bet of the Century," out Tuesday.
• Engineering, PR, and legal employees worried Musk was overstating Autopilot's abilities in 2016.

Elon Musk has caught heat for years over the way he exaggerates the capabilities of Tesla's driver-assistance features: Autopilot and Full Self-Driving. Autopilot doesn't pilot cars automatically, and Full Self-Driving doesn't make them autonomous.

Most of that criticism has come from safety advocates, politicians, and others in the auto industry who say Tesla's fast-and-loose approach to automated-driving tech puts people in danger. Making overly optimistic promises about what these systems can or will be able to do emboldens people to misuse them and causes crashes, they argue.

But some of the earliest such concerns came from within Tesla, according to Tim Higgins' "Power Play: Tesla, Elon Musk, and the Bet of the Century," a new book on the automaker's history, published Tuesday.

As Tesla geared up to release a new version of Autopilot hardware and software in late 2016 - a year after the system first hit streets - Sterling Anderson, who led the Autopilot team, grew increasingly worried about Musk's tendency to overpromise, according to people familiar with his team's work.

Anderson knew that the system, even with the upgraded features he was working on, wouldn't be able to take total control of a vehicle. Autopilot was and is mainly geared toward highway driving, using an array of cameras and sensors to keep a car in its lane and maintain a set distance to the car ahead.

He was afraid Musk would declare it fully self-driving and relayed his concerns to Jon McNeill, Tesla's then head of sales and marketing, according to the book.

Read more: Elon Musk said he hates being Tesla's CEO. Here are 9 top candidates who could replace him if he stepped down.

Employees in Tesla's legal and public relations departments shared Anderson's concerns. For a year they had struggled to keep Musk on-message that drivers needed to keep their hands on the wheel when using Autopilot, according to people with knowledge of those conversations. Musk repeatedly took his hands off the wheel when taking TV reporters out for test drives.

Making matters worse, in May of that year a 40-year-old named Joshua Brown was killed when his Tesla Model S rammed into a tractor-trailer that was crossing the road. He had Autopilot switched on and wasn't paying attention. It would be the first of many similar incidents that would put Tesla's technology under the microscope.

Sure enough, when Tesla released the next generation of Autopilot in October 2016, Musk said that all new vehicles would come with hardware that would eventually allow for full autonomy. He put forth the bold claim that a Tesla would be able to pilot itself coast-to-coast by the end of 2017.

Musk's remarks didn't sit well with some engineers who "didn't think what he was proposing was possible," Higgins writes. Tesla's higher-ups weren't happy either, especially given Musk's tendency to lash out when his expectations weren't met.

"They knew not only that his timeline wasn't tenable, but that he'd be looking for someone to blame soon enough," Higgins writes. "His promises struck some as crossing a new line."

Almost five years on, Tesla still hasn't completed its autonomous road trip - no car company has even come close. Musk has continued to aggressively push Tesla's Full Self-Driving tech forward, releasing a still-buggy beta version of the software to thousands of the company's most loyal customers.