P0400 code came back on, after cleaning EGR and new vacuum lines, why?

Question

Check engine light scanned P0400, I removed and cleaned EGR valve and ports to exhaust and intake manifold, all clean, replaced vacuum lines with new and check engine light stayed off for 2 weeks, but came on again today and scanned code P0400 again, why?

Answer 1

maybe a solenoid valve  is not opening here are diagnostic procedures from the manual