The suit, filed by Martha Avila's daughter and son-in-law, named both Tesla and that car's driver as defendants.
The driver, identified by the Harris County Sheriff's Office as 44-year-old Michael Butler, didn't respond to a text message seeking comment late Tuesday. No one answered at his Fort Bend County home.
Investigators say he told them the car was in autopilot mode when it plowed into the house Friday.
On Tuesday, the sheriff's office said its investigation had yet to uncover evidence of a "mechanical malfunction."
But in the lawsuit, attorneys write that "the Vehicle ... was defective in design and unreasonably dangerous," claiming the car may have accelerated by itself.
"We're still in a fact-finding mode, but mainly we're alleging a product defect and a failure to warn on Tesla's part," said attorney Chris Adkins.
Tesla has so far ignored all requests for comment from Eyewitness News.
But Monday, the company's vice president of AI, wrote on X that "the driver manually overrode self-driving by pressing the accelerator all the way to 100% of the accel pedal ...and had the accelerator pressed even after the crash."
"Tesla's statement, in my opinion, is a little bit fishy given that they indicated the accelerator was pushed at 100 percent all the way through the collision until the vehicle stopped and beyond," said Adkins. "If that were the case, he would have had his foot on the accelerator all the way through the crash until the vehicle came to a stop. If that's the case, he should have a shattered leg."
The lawsuit demands Tesla preserve its black box data, autopilot system data and camera footage.
The National Highway Traffic Safety Administration is also investigating the crash.
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