MARKTAB, I admire you for your knowledge and analytical acumen! I guess I read elsewhere "help/ info"- to test if the EGR valve or its pipe is the culprit for code P400 one could feel if the valve is sliding without binding by moving the sliding part up and down while the engine is running! Was the author kidding? Let alone while engine is running, one cannot have access to the valve even when the engine is shut off! May be I got the whole thing wrong? i would appreciate clarification. thank you very much if any one else also can give some insight into this matter.