The NHTSA has opened a formal safety probe into Tesla Autopilot after a series of crashes involving emergency vehicles, Reuters reported Monday.

The probe covers an estimated 765,000 vehicles from model years 2014 to 2021, including Tesla Model S, Model X, Model 3, and Model Y EVs, according to the report.

The agency said that since January 2018 it had identified 11 crashes in which Tesla electric cars struck emergency vehicles at "first responder scenes," resulting in 17 injuries and one death.

Of those crashes, four happened this year, with the most recent one occurring last month in San Diego, according to the report. All involved vehicles were confirmed to have Autopilot or Traffic Aware Cruise Control operating when approaching the crash sites, the NHTSA said in a document cited by Reuters.

2021 Tesla Model X

2021 Tesla Model X

The NHTSA said that most crashes took place after dark at scenes with flashing lights, illuminated flares and signs, and road cones. The probe will look at "methods used to monitor, assist, and enforce the driver's engagement," according to the agency.

Autopilot can handle acceleration, steering, and braking in certain situations, but still requires an attentive driver. Getting drivers to pay attention is inherently challenging, leading other automakers, such as Lucid Motors, to embrace driver-monitoring cameras for similar systems.

Tesla recently introduced a new driver-assist sensor suite for the North American-market Model 3 and Model Y, eliminating radar in favor of a camera-only approach.

The automaker also recently introduced a subscription version of the more advanced Full Self-Driving system. Despite the name, and Tesla CEO Elon Musk's past claims that gradual upgrades would enable autonomous driving, this version is also firmly in the realm of driver-assistance, and requires an attentive driver behind the wheel at all times.