Code P0401?

My Beetle is a TDI, not sure if that matters. I bought this car used. When I first bought it, the test drive went good runs great. I drove it 2 hours back to my home and 10 minutes before I got there the check engine light came on. I scanned it and it showed P0401 and the other was the one for the DPF. I had the dealer inspect the car and they cleaned the DPF and cleaned the EGR valve. After receiving the car again, I drove the car another 2 hours home, all good. In the morning it got driven for 30 minutes then the light came back on, scanned the car again for codes and P0401 came back up. Sent back to the dealer, they now have replaced the EGR valve. So, after receiving the car again and driving 2.5 hours, all good. This morning after 10 minutes of driving the car, the engine came back on. I will scan the codes this afternoon and update. If it is the P0401, any ideas on what I can do?