How safe is it to leave a car’s automatic transmission in Park (P) position without engaging the parking brakes?
If there is no mechanical flaw in the car, it should not roll away in Park. But if the auto gearbox is defective, leaving the lever in P may not lock the vehicle in position.
There are instances when a transmission’s D (Drive) or R (Reverse) does not engage either. This may be a linkage problem. The same thing could happen in P (Park), rare as it may be.
So to be safe, it would be best to engage your car’s parking brakes and turn off the engine, even if you are just leaving the vehicle momentarily.