Elon Musk on Monday panned a pilot version of an advanced driver-assistance feature Tesla Inc. is developing, a week after U.S. car-safety regulators opened a probe into a more basic iteration of the company’s driving aide.

The statement amounts to a public concession by the Tesla CEO of a shortcoming in a driver-assistance feature designed to help vehicles steer through urban areas. The feature, available on a relatively small number of vehicles as part of a pilot program, is part of what Tesla calls Full Self-Driving, or FSD, technology.

“FSD Beta 9.2 is actually not great,” Mr. Musk said via Twitter, adding the company “is rallying to improve as fast as possible.”

Elon Musk Reveals Tesla Plans for Humanoid Robot During AI Day

At Tesla’s AI Day, Elon Musk said the company plans to build a robot in human form that would draw on some of the technology for its vehicles. The event comes as U.S. auto safety regulators are investigating Tesla’s advanced driver-assistance system. Photo: Tesla The Wall Street Journal Interactive Edition

Tesla vehicles come equipped with driver-assistance technology the company calls Autopilot. The features leverage cameras and other sensors to help drivers with tasks such as maintaining a safe distance from other cars on the highway. Tesla also sells an upgraded suite of features, FSD, for $10,000. It is intended to provide greater functionality. The technology doesn’t yet allow for autonomous driving.

Tesla’s driver-assistance technology has drawn scrutiny from safety officials and lawmakers. The National Highway Traffic Safety Administration, which regulates auto safety, last week said that it was investigating Autopilot in the wake of 11 crashes since January 2018 involving Teslas at scenes to which emergency vehicles had responded. Such probes can but don’t always result in recalls. [

Days later two U.S. senators asked the Federal Trade Commission to investigate whether Tesla has been deceptive in its marketing of Autopilot and FSD. Tesla hasn’t responded to requests for comment on the safety probe and lawmakers’ request to the FTC.

Mr. Musk has long defended Tesla’s driver-assistance technology. “Tesla with Autopilot engaged now approaches 10 times lower chance of accident than average vehicle,” he tweeted in April. He previously called safety the company’s “primary design goal.”

He last week doubled down on Tesla’s embrace of artificial intelligence at a recruiting event where he said the company was working on a humanoid robot and that a prototype could be ready next year. 

Mr. Musk has commented before on the difficulty of developing fully autonomous vehicles. “Generalized self-driving is a hard problem, as it requires solving a large part of real-world AI. Didn’t expect it to be so hard, but the difficulty is obvious in retrospect,” Mr. Musk said on Twitter last month.

On an earnings call last month, Mr. Musk said, “We need to make full self-driving work in order for it to be a compelling value proposition.”

Tesla didn’t respond to a request for comment on what specific concerns the CEO had with the software.

Write to Rebecca Elliott at rebecca.elliott@wsj.com