A car that's lacking is really soft. Cars need to be hard so that things like bugs and other cars wont hurt the people inside when you hit them. But if your car is lacking the hardness it needs, you'll have a really soft, useless car.
This car is probably so soft because it's made entirely of naan (なん). Naan may be delicious, but it makes a really crappy car. No wonder it was so soft (and yummy).
Currently there are no similar looking kanji which exist in the WaniKani learning system