Translation:I am walking because I do not have a car.
Not sure how old this question is but for the reference of anyone else, I've heard that "no tengo coche" is actually short for "no tengo ningún coche" which would be the grammatically correct way to say it. But besides, native speakers often omit the indefinite article with verbs like tener and haber. Ex. ¿Tienes lápiz? (Do you have a pencil?)
Just one of those things about spanish. I think of it as, "I have no car." But I used to get dinged for translating it that way, so I stopped doing that. I've been curious if there is a way in spanish to say, "I have no car" as distinct from, "I don't have a car." as distinct from, "I don't have one car." It doesn't seem like there is. Makes you realize how complicated English is.