There is a rubber vac hose going to your EGR diaphragm. Check to see if there are any holes or cracks in it.
Remove your EGR sensor and see if it's caked with carbon. I'm not sure that that would cause the error you're having, but it never hurts to clean it anyway.
Lastly, you can remove your EGR valve and suck on the diaphragm to see if the shutter is opening and closing.