Like many of our dreams, this dream should not be taken literally.
The black car and the black snake (and black animals, in general) are positive signs in this dream. This is because the color black is, in mythology, associated with the underworld. And the mythological underworld is a symbol for the unconscious. The exploration of this unconscious is a trait of the more spiritually and psychologically developed.
In this dream, the car would be your means of traveling through this lower realm. The snake is a symbol of spiritual power.
As for the dog -- it is the dog that guards the gate to the underworld. Its death means that the gate of the underworld is now open for your exploration.