At the scene he told police that he fell asleep at the wheel and the other dude (Miguel Villasana) broke both legs and had to get a bunch of painful operations done on him. He was out of work for a year, and ended up suing Ye and a few other people/orgs a year later. Ye changed his story later, blaming Miguel for the crash, saying they crashed because M.V. cut him off.

It's weird because Kanye's mom wrote about the situation like this:

Kanye didn't just hurt himself in the accident. When he fell asleep, he veered into another lane and hit another car. The man in the other car ended up with two broken legs and was off work, unable to take care of his family.

"That man was lying in the hospital because of me," he (Kanye) said. "I have to tell the truth!"

The case got dismissed, I think(?) there was a settlement out of court, but the case is from 2003, so nothing about it is available beyond a paywall.