How do I troubleshoot a P0400 EGR?

2011 Ford Escape V-6. 130,000 mi.
My daughter lives 4 hours away. She dropped by a couple weeks ago with a p0400 EGR code. And water pump problems. I didn’t have time to do proper diagnosis, so I shotgunned and replaced electric EGR valve. I cleared codes and it was good for over a week. Now the P0400 is back. She’s visiting again another short one and I would like some help to quickly diagnose this. All I know what to do is
1: make sure the exhaust tube is not leaking.
2: check connector
3: make sure gasket is sealing.
4: activate egr with scanner and watch map sensor?
I read #4 online. What else am I missing?