The National Highway Traffic Safety Administration (NHTSA) said it was opening an investigation after the agency identified concerns due to crash events after vehicles had the recall software update installed "and results from preliminary NHTSA tests of remedied vehicles."

The agency's new probe comes after it closed its nearly three-year investigation into Autopilot, saying it found evidence that "Tesla’s weak driver engagement system was not appropriate for Autopilot’s permissive operating capabilities" that result in a "critical safety gap."

NHTSA also cited Tesla's statement "that a portion of the remedy both requires the owner to opt in and allows a driver to readily reverse it."

The agency said Tesla has issued software updates to address issues that appear related to its concerns but has not made them "a part of the recall or otherwise determined to remedy a defect that poses an unreasonable safety risk."

Tesla said in December's its largest-ever recall covering 2.03 million U.S. vehicles - or nearly all of its vehicles on U.S. roads - was to better ensure drivers pay attention when using its advanced driver assistance system.

The new recall investigation covers Model Y, X, S, 3 and Cybertruck vehicles in the U.S. equipped with Autopilot produced between the 2012 and 2024 model years, NHTSA said.

Tesla said in December Autopilot's software system controls "may not be sufficient to prevent driver misuse" and could increase the risk of a crash.

The auto safety agency disclosed Friday that during its Autopilot safety probe it first launched in August 2021 it identified at least 13 Tesla crashes involving one or more death and many more involving serious injuries in which "foreseeable driver misuse of the system played an apparent role."

NHTSA also on Friday raised concerns about Tesla's Autopilot name "may lead drivers to believe that the automation has

greater capabilities than it does and invite drivers to overly trust the automation."

Tesla did not immediately respond to a request for comment.

In February, Consumer Reports, a nonprofit organization that evaluates products and services, said its testing of Tesla's Autopilot recall update found changes did not adequately address many safety concerns raised by NHTSA and urged the agency to require the automaker to take "stronger steps," saying Tesla's recall "addresses minor inconveniences rather than fixing the real problems."

Tesla's Autopilot is intended to enable cars to steer, accelerate and brake automatically within their lane, while enhanced Autopilot can assist in changing lanes on highways but does not make vehicles autonomous.

One component of Autopilot is Autosteer, which maintains a set speed or following distance and works to keep a vehicle in its driving lane.

Tesla said in December it did not agree with NHTSA's analysis but would deploy an over-the-air software update that will "incorporate additional controls and alerts to those already existing on affected vehicles to further encourage the driver to adhere to their continuous driving responsibility whenever Autosteer is engaged."

NHTSA's then top official, Ann Carlson, said in December the agency probe determined that more needed to be done to ensure drivers are engaged when Autopilot is in use. "One of the things we determined is that drivers are not always paying attention when that system is on," Carlson said.

NHTSA opened its August 2021 probe of Autopilot after identifying more than a dozen crashes in which Tesla vehicles hit stationary emergency vehicles.

NHTSA said in December it found Autopilot "can provide inadequate driver engagement and usage controls that can lead to foreseeable misuse."

Separately, since 2016, NHTSA has opened more than 40 Tesla special crash investigations in cases where driver systems such as Autopilot were suspected of being used, with 23 crash deaths reported to date.

Tesla's recall includes increasing prominence of visual alerts and disengaging of Autosteer if drivers do not respond to inattentiveness warnings and additional checks upon engaging Autosteer. Tesla said it will restrict Autopilot use for one week if significant improper usage is detected.

Tesla disclosed in October the U.S. Justice Department issued subpoenas related to its Full Self-Driving (FSD) and Autopilot. Reuters reported in October 2022 that Tesla was under criminal investigation.

Tesla in February 2023 recalled 362,000 U.S. vehicles to update its FSD Beta software after NHTSA said the vehicles did not adequately adhere to traffic safety laws and could cause crashes.