The requirements for an emissions test can vary depending on the state you live in. Currently, more than 30 states require some level of testing on registered vehicles. To know if you need an emissions test, you should contact your states environmental agency for accurate, up-to-date information. However, some general requirements for an emissions test include:

• Certificate of vehicle registration
• Prior inspection report
• Letter from the department that oversees the emissions testing program in your city or state
• Renewal notice, which you may have received via mail, eNotify, or email

In addition to these documents, some states may require you to bring the appropriate test fee, the key for locking the gas tank, and the previous years vehicle registration, title, or bill of sale. To ensure that your vehicle passes the test, you should prepare it beforehand by warming up the engine, turning off the air conditioner, and making sure the "Check Engine" light is off. Other preparations that can help your vehicle pass the test include having fresh fuel, getting an oil change, having a tune-up, and making sure your vehicle is at the proper operating temperature.