Newbie fail

I just bought a 2012 prius. 2 days after purchase I get the P0401 code with cel. The ran good and still does. I'm assuming egr system needs cleaned and I may end up with a bad head gasket soon. I am also assuming the dealership knew this since the cel came on after 3 trips since I bought it. My question is are there any scenarios where you get P0401 and the car doesn't run bad or have death shakes and the P0401 is not caused by the normal culprits?

 

The p0401 code erased by itself the next day, it had no pending codes stored and cel was not on. Couple days later light came back on then it cleared its self again the next day. I check for pending codes after each trip. It only shows a pending code on my trip to work. I have to drive the car hard to work because I'm on call. I have a hour commute it's 47 miles each way 1/3 curvy country roads and 2/3 highway with a couple steep long hills. On the drive back I drive slow and easy and it didn't post a pending code when I cleared the pending code from the drive to work. I have only self cleared the code once. I am wondering with its smooth engine sound and driving if it could be something other than egr.

 

I forgot to add I I bottomed the car out on the way to work it broke the exhaust mount after the converter and broke the heat shield. It caused a rattle I secured the heat shield back to the bolt and rattle is gone. Could the exhaust bottoming out cuase a p0401 code?