If the EGR flow is insufficient; that can be caused by carbon deposits clogging the EGR valve, supply line, or manifold passages. The way to fix this is to remove the EGR valve, and scrape the carbon out of all the openings. Spraying throttle body cleaner into the parts may help to get the dirt out. Be sure to move the valve through the full range of its travel, to insure it is not sticking. If the EGR line is clogged, that part can be bought new; rather than trying to snake a tool through the long, narrow metal line.
But this problem can also be caused by vacuum leaks in any of the hoses which carry the vacuum signal to the EGR valve; or by a defective EGR vacuum solenoid; or by a defective EGR valve position sensor (also called a pressure feedback sensor). Some of these parts have an electrical and a vacuum portion. So if these parts are not working; it could be either an electrical or a vacuum problem. This is why having access to the diagnostic procedures in a factory or a professional grade service manual can save lots of time and trouble.
Once the problem is corrected; the trouble code will remain in the car's computer until it is reset by a code scanner.