An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Vehicle and Engine Certification

Manufacturer Information, Guidance Letters and Advisory Circulars for Vehicle, Engine, and Equipment Programs


Search for documents in EPA's Transportation & Air Quality database:
On this page:

Overview of Manufacturer Information and Guidance Letters

These letters provide information, guidance, and instructions to the regulated industry on specific compliance topics and issues.

Find Letters by Year They were Issued

The links below will take you to all the letters that were issued for that year.

Top of Page

How to Get Notified when New Letters are Issued

EPA uses a list server to notify manufacturers when a manufacturer information or guidance letter has been issued.

The list server notice:
  • Goes out to the entire list server distribution list;
  • Uses the subject line to specify to which industry(s) the letter applies; and
  • Provides the website location for viewing and/or downloading the new guidance letter.

Subscribe to List Server

To join the "manufacturer-info" list server, send an email to

Unsubscribe from List Server

To unsubscribe from the " manufacturer-info" list server, send a blank email message to:

Advisory Circulars

Advisory Circulars provide more background information about many issues associated with new vehicle and engine compliance.

Top of Page