The Autopilot feature in Tesla vehicles can be tricked into operating without a driver, an influential consumer magazine in the US has found.
Consumer Reports engineers looked into claims that Autopilot can operate without a driver present.
They tested the Model Y on a closed track and concluded the system could be "easily tricked".
It comes days after a fatal Tesla crash in Texas. Police believe no one was in the driver's seat.
Tesla's Autopilot is an advanced driver assistance system that Tesla says "enhances safety and convenience behind the wheel".
The Consumer Reports team said they successfully - and repeatedly - tricked the car into driving their test track with no one in the driver's seat.
"In our evaluation, the system not only failed to make sure the driver was paying attention, but it also couldn't tell if there was a driver there at all," said Consumer Reports auto testing director Jake Fisher.
"It was a bit frightening when we realized how easy it was to defeat the safeguards, which we proved were clearly insufficient."
Tesla's website says the Autopilot system requires a "fully attentive driver" and using the system does not make the car autonomous.
Some of the safety requirements for Autopilot mode include: keeping the driver's hands on the steering wheel, buckling the seatbelt and not opening any doors.
On Saturday, two men were killed after a Tesla car crashed into a tree and caught fire in Texas.
The victims were found in the front passenger seat and in the back seat of the vehicle, leading police to believe nobody was in the driver's seat.
However, Tesla boss Elon Musk said that "data logs recovered so far show Autopilot was not enabled".
"Moreover, standard Autopilot would require lane lines to turn on, which this street did not have," Mr Musk tweeted.
Your research as a private individual is better than professionals @WSJ!— Elon Musk (@elonmusk) April 19, 2021
Data logs recovered so far show Autopilot was not enabled & this car did not purchase FSD.
Moreover, standard Autopilot would require lane lines to turn on, which this street did not have.
On Thursday, two Democratic Senators sent a letter to the US National Highway Traffic Safety Administration (NHTSA) asking them to investigate the fatal Tesla accident in Texas.
Senator Blumenthal and Senator Markey also requested a report outlining ways to prevent future accidents.
The NHTSA has opened investigations into 28 crashes involving Tesla vehicles.
Tesla has not responded to the BBC's request for comment.
Follow Cody Godwin on Twitter at @MsCodyGodwin