Which number contains a sentence error?

1.Although Milo saved all his money from summer jobs, he and his brother haven't gotten that motorcycle yet.
2.Milo saved all his money from summer jobs. He and his brother haven't gotten that motorcycle yet.
3.Milo saved all his money from summer jobs, he and his brother haven't gotten that motorcycle yet.
4.Milo saved all his money from summer jobs, but he and his brother haven't gotten that motorcycle yet.