Only the car as a functioning whole system has these properties. This popular saying is much deeper than it might first appear. When we say that the whole is more than the sum of its parts, we mean that the whole system has qualities that are different than those of the parts. The whole is qualitatively different, which is a much more important difference than a mere increase in quantity. Take water as another example of a system.
Water is made of hydrogen and oxygen.
At normal temperatures and pressures, they are both gases. Hydrogen is highly explosive and fire requires oxygen. Put them together and you have a liquid that extinguishes fires.