1-My car is broken.
2-My car is broken down.
Which of these sentences mean:
a-My car is damaged so badly that it won't run.
and which can be used if
b-My car is not seriously damaged (maybe something is wrong with the door...)
Both mean that something is preventing your car from operating, so it will be a mechanical fault and not just something wrong with the door. We do not usually say the car is broken - if it has been in an accident, we would probably say "My car is smashed up"; "My car is a write-off".