What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Mechanic instructor and student started up the airplane for a "taxi check". The brakes were held by the mechanic in the left seat. The aircraft brakes failed to hold the aircraft after the engine was started. After moving forward for a few feet, the left brake partially engaged and the aircraft unexpectedly turned to the left. The aircraft could not be stopped by the brakes. The aircraft came to rest after a low speed impact with a parked car was made. The engine never stopped running, and the propeller made repeated contact with the brush guard of the parked truck. The mechanic secured the engine.
As the FAA filed it
MECHANIC INSTRUCTOR AND STUDENT STARTED UP THE AIRPLANE FOR A "TAXI CHECK". THE BRAKES WERE HELD BY THE MECHANIC IN THE LEFT SEAT. THE AIRCRAFT BRAKES FAILED TO HOLD THE AIRCRAFT AFTER THE ENGINE WAS STARTED. AFTER MOVING FORWARD FOR A FEW FEET, THE LEFT BRAKE PARTIALLY ENGAGED AND THE AIRCRAFT UNEXPECTEDLY TURNED TO THE LEFT. THE AIRCRAFT COULD NOT BE STOPPED BY THE BRAKES. THE AIRCRAFT CAME TO REST AFTER A LOW SPEED IMPACT WITH A PARKED CAR WAS MADE. THE ENGINE NEVER STOPPED RUNNING, AND THE PROPELLER MADE REPEATED CONTACT WITH THE BRUSH GUARD OF THE PARKED TRUCK. THE MECHANIC SECURED THE ENGINE.