The Star Trek actor was found pinned against a mailbox pillar and security fence by his Jeep Grand Cherokee
The Russian-born actor was discovered by friends pinned against a mailbox pillar and security fence by his Jeep Grand Cherokee early on Sunday.
Investigators said the 27-year-old actor got out of the vehicle before it rolled backwards down the steep driveway towards him.
Yelchin died of accidental blunt force asphyxia, Los Angeles County Coroner Assistant Chief Ed Winter told Reuters.
The US National Highway Traffic Safety Administration (NHTSA) said in February that 2015 models of the vehicle - like Yelchin's - could continue to move after drivers thought they had locked them in "park", and linked the issue to more than 100 crashes.
Fiat Chrysler Automobiles US unit issued a recall for hundreds of thousands of Jeep Grand Cherokees and other models in April to address the problem.
However, FCA US said it had not found a permanent remedy and mainly advised owners to double check that their car was in "park" as intended.
The NHTSA said: "Drivers thinking that their vehicle's transmission is in the 'PARK' position may be struck by the vehicle and injured if they attempt to get out ... while the engine is running and the parking brake is not engaged."
No deaths have previously been linked to the problem, but injuries reported included fractured bones and others that required hospital treatment.
"It is premature to speculate on the cause of this tragedy," the manufacturers said in a statement, adding that it was investigating further.
Yelchin moved to the US when he was six months old with his parents, who were star figure skaters with the Leningrad Ice Ballet, and made his film debut at age nine in A Man Is Mostly Water.
His breakout performance came in the 2006 crime thriller Alpha Dog, and his movie credits include JJ Abrams' three Star Trek films and last year's critically acclaimed Green Room.
Abrams described Yelchin as "funny as hell and supremely talented", while Star Trek co-star Zachary Quinto said the actor was "one of the most open and intellectually curious people" he knew.
"So enormously talented and generous of heart. Wise beyond his years, and gone before his time," Quinto posted on Instagram.
Susan Sarandon, who starred alongside Yelchin in the 2008 coming-of-age comedy Middle Of Nowhere, described the actor as "an original".
"One of the most curious, funny, sweet people I've ever known," she wrote on her Facebook page.
"He was a searcher, an incredible talent and a loyal and loving son.
"Any time would be too soon for his departure from this plane, but this is an unforgivable and unbearable loss."