What is Automatic Visa Revalidation?
People holding certain immigration statuses, including J-1, may re-enter the U.S. using an expired visa stamp if they travel to Canada, Mexico, or adjacent islands for 30 days or less.  Please keep the following things in mind if you intend to use Automatic Visa Revalidation: 

• Your passport should be valid. If your expired visa stamp is in an old passport, you should bring the old passport as well to present upon re-entry.
• Your immigration status must not be expired in order to use this. This means that you must have a valid, unexpired I-94 record.
• You cannot use Automatic Visa Revalidation if have a pending visa stamp application with a consulate. 
• If you have been denied a new visa stamp, you cannot use Automatic Visa Revalidation. 
• If you travel to any other countries except Canada, Mexico, and/or any adjacent islands on this trip, you cannot use Automatic Visa Revalidation. 
• If you are a national from a state sponsor of terrorism, you cannot use Automatic Visa Revalidation. 
• If you travel to Cuba on this trip, you cannot use Automatic Visa Revalidation. 
• If required, make sure you have the appropriate visa to enter the country you are visiting.
• J-1s and J-2s must have a travel endorsement signature on their DS-2019 from within the last 6 months. 
• Your I-94 card should NOT be taken from you upon exiting the U.S. (if you have a paper I-94 still). If an airline official or U.S. Immigration officer tries to remove the I-94 card, it may be necessary to inform them that your visit will be less than 30 days. 
• Be prepared to answer the questions regarding your eligibility for automatic revalidation on the date of re-entry, including maintenance of current status and non-immigrant intent (if applicable; H-1Bs are not required to prove non-immigrant intent)
• If you are a J-1 or J-2, you may be required to provide financial documentation that matches what is listed on your DS-2019.
• If you will be traveling by air, you should confirm that your airline is familiar with the visa revalidation process and will issue you a boarding pass when returning to the U.S. even though you have an expired U.S. visa in your passport.
• If you've changed immigration statuses in the US since your last admission (for example, F-1 to H-1B or J-1 to H-1B), you may still benefit from AVR: "In cases where the original nonimmigrant classification of an alien has been changed by DHS to another nonimmigrant classification, the validity of an expired or unexpired nonimmigrant visa may be considered to be automatically extended to the date of application for readmission, and the visa may be converted as necessary to that changed classification." See 22 CFR 41.112(d)(1)(ii). 

See the following websites for more information: 

• U.S. Department of State - Automatic Visa Revalidation
• Customs and Border Patrol - Automatic Visa Revalidation
• For F and M nonimmigrants

Legal Citation: 22 CFR 41.112(d)
List of Adjacent Islands: INA, Section 101(b)(5) - to find list, press Ctrl+F, then type "adjacent islands" into the search bar