All mechanics must be certified in order to work on vehicles for compensation. This includes diagnosing problems, replacing parts or adjusting vehicles to operate differently. Certification is done at the state level. A test must be passed after proper schooling or apprenticeship and a fee must be paid before receiving a certificate.
The National Institute for Automotive Service Excellence (ASE) is another certification body. Its certification cannot be used in lieu of state certification. However, the exams offered by the ASE award specialty certificates that can show expertise in a certain area. This can be in transit buses or heavy trucks, for example. A certificate in a specialized area can help mechanics obtain employment with companies that service these types of vehicles.
Aviation mechanics must also graduate from school and pass a written exam before receiving certification from the state. It is also necessary to do this before working for a profit. Schooling must be done at an accredited school, such as the Carolina Aeronautical A & P, which has both national and regional accreditation.