US car safety regulators have asked Tesla why it failed to recall its vehicles to update its Autopilot driver-assistance system instead of using an over-the-air software update.
The National Highway Traffic Safety Administration (NHTSA) has also questioned the Elon Musk-run company's requirement to use non-disclosure agreements (NDAs) for beta testing its software.
The issues were raised in two separate letters sent to the company as the NHTSA continues a formal investigation into the Autopilot system after crashes involving Teslas and stationary emergency vehicles.
The probe came after the agency identified 12 crashes since 2018 where Teslas "have encountered first responder scenes and subsequently struck one or more vehicles involved with those scenes", it said at the time.
In the first letter, the NHTSA makes it clear it considers a software update related to vehicle safety requires a recall and wants to know the "technical and/or legal basis for declining" to do so.
"As Tesla is aware, the Safety Act imposes an obligation on manufacturers of motor vehicles to initiate a recall by notifying NHTSA when they determine vehicles or equipment they produced contain defects related to motor vehicle safety or do not comply with an applicable motor vehicle safety standard," the agency said.
Tesla also failed to file a recall notice within the five working day period following the identification of the safety issue and issuing the over-the-air update.
"Any manufacturer issuing an over-the-air update that mitigates a defect that poses an unreasonable risk to motor vehicle safety is required to timely file an accompanying recall notice to NHTSA," the agency wrote.
Despite its name, 'Autopilot' doesn't take full control of the vehicle and still requires the driver to keep their hands on the wheel at all times.
Each Tesla ships with a basic driver assistance system but for an extra US$10,000 owners can purchase full self-driving (FSD) software that Musk has said will deliver full autonomous driving in the future.
The second letter indicated the NHTSA had recently become aware of reports that participants in Tesla's FSD beta program had to sign NDAs that limit participants from sharing information that portrays it negatively.
"Given that NHTSA relies on reports from consumers as an important source of information in evaluating potential safety defects, any agreement that may prevent or dissuade participants in the early access beta release program from reporting safety concerns to NHTSA is unacceptable," the agency wrote.
"Moreover, even limitations on sharing certain information publicly adversely impacts NHTSA's ability to obtain information relevant to safety."
NHTSA had previously investigated Autopilot in 2017 but decided to take no action. The current probe encompasses the 765,000 vehicles with Autopilot in the US built since 2014.
Tesla has until November 1 to respond to the NHTSA's letters and is liable to be fined tens of thousands of dollars every day if it fails to do so.