Pay off the 401k loan. That 20k that is outstanding is money that ISN'T in the market and earning in your 401k. The expected return on that is much better than the 1.9% car note.
Another important reason: If you are terminated/quit many 401k's have a provision that the outstanding loan balance is due immediately. If you couldn't pay that off with cash on hand, even more reason to wipe out that loan. A standard car note can never be advanced to a balloon payment like that.