Jeremy Renner Snowplow Accident, Police Report Reveals New Details

New details have emerged in Jeremy Renner's horrific snowplow accident ... police say he was indeed trying to save a family member when the snowcat vehicle crushed him, and there are signs the machine was malfunctioning.

The "Hawkeye" star was attempting to stop the vehicle from sliding and hitting his grown nephew on January 1 -- according to the redacted police report, obtained by CNN ... noting the emergency brake wasn't engaged when it started sliding.

Washoe County Sheriff’s Office says the brake would've stopped the machine from moving ... but the brake indicator light inside the cab of the vehicle wasn't functioning -- indicating mechanical issues might've also been a factor.

The report says Renner would've had to climb directly onto the plow's moving track in order to get back into the cab, which is when cops say he was "immediately pulled under" by the machine as it continued down the road.

It says the actor focused on breathing after getting crushed while his nephew helped him until medical professionals arrived. The report also says drug or alcohol impairment was ruled out as a factor.