What is a corrosion or rust warranty?

A corrosion warranty covers rust-through, meaning holes that rust all the way through a body panel, for a set period that is often longer than the basic warranty. It usually does not cover surface rust, cosmetic paint issues or corrosion caused by damage, so read the exact wording. Coverage lengths vary by manufacturer and sometimes have no mileage limit. If you live where roads are salted in winter, regular washing helps, and keep records in case you ever need to file a claim.