EGR P0327 code

My first question pertains to the check engine light. When I scan it, the code p1404 comes up, which is an EGR valve code. I replaced the EGR valve 4 times and it still reads this problem. What is going on? Is it just a problem with the system?2001 Pontiac Grand Prix 1)The check engine light wont go off and its reading a problem with the EGR valve 2)where is the knock #1 sensor located?

My second question is about the p0327 code, I don't believe that this code is causing the check engine light to come up, but I still need to know where the knock #1 sensor is located on my car.