(Reuters) -Influential U.S. magazine Consumer Reports said on Thursday its engineers were able to operate a Tesla Inc vehicle without anyone in the driver's seat, but the system failed to send out a warning or indicate that the driver's seat was empty.
The engineers tested a Tesla Model Y this week as investigators probe an accident where two men died after their Tesla Model S, which was believed to be operating without anyone in the driver's seat, crashed into a tree on Saturday night north of Houston.
Over several trips across half-mile closed test track, the Model Y automatically steered along painted lane lines, the magazine said.
"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 Jake Fisher, senior director of Consumer Reports' auto testing.
"Tesla is falling behind other automakers like GM and Ford that, on models with advanced driver assist systems, use technology to make sure the driver is looking at the road."
Tesla's Autopilot is a driver assistance system that handles some driving tasks and allows drivers to take their hands off the steering wheel at times, but Tesla says its features "require active driver supervision and do not make the vehicle autonomous."
Tesla did not immediately respond to a Reuters request for comment.
The Consumer Reports story comes amid growing scrutiny over Tesla's semi-automated driving system following recent accidents and as it is preparing to launch its updated "full self-driving" software to more customers.
Separately on Thursday Senators Richard Blumenthal and Ed Markey sent a letter to the National Highway Safety Administration's (NHTSA) acting administrator asking the agency to thoroughly investigate the Texas accident and produce a report outlining corrective actions to prevent future accidents.
NHTSA said Monday it was sending a special crash investigation team to probe the crash and has opened 28 crashes into Tesla crashes to date, with four pending. NHTSA did not immediately comment on the letter.