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Vehicle and Engine Certification

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


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Overview of Guidance Letters

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

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Find Guidance Letters by Year They were Issued

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

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How to Get Notified when New Letters are Issued

EPA uses a list server to notify manufacturers when a 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 "guidance_letter" list server, follow these steps:
  1. Go to the: Subscribe page
  2. On this page, enter your email address (name and password are optional).
  3. Click the "subscribe" button on the bottom right.
  4. You will then be directed to a confirmation page that states:
    "Subscribe requested. You will receive an email acknowledgement in a few minutes. Please check your email account for the acknowledgement email."
  5. In order to complete your subscription request, you must follow the instructions in the acknowledgement email.
  6. After following the instructions, please allow up to a few hours for your subscription to process.
  7. Once your subscription is processed, you will receive a welcome email that contains general information about the list server.

Unsubscribe from List Server

To unsubscribe from the "guidance_letter" list server, send a blank email message to:

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Advisory Circulars

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

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