As a diesel mechanic, you maintain and repair diesel-powered vehicles and equipment. In addition to buses and trucks, you may also work with cranes and other industrial equipment. Some diesel mechanics work on personal cars and light vehicles that have diesel engines. As an entry-level diesel mechanic, you typically undergo on-the-job training where you learn the skills to handle the responsibilities of a professional mechanic. You assist journey-level mechanics as they perform repair or maintenance duties. You also test repairs and ensure that the vehicle meets local and federal laws that regulate variables like efficiency and emissions.