The "Service Engine Soon" light lits up on the dashboard of my 1997 Nissan Maxima. I went to O'Reily and borrowed their AutoXray ODBII Reader. The reader returned trouble code P0400 "Exhaust Gas Recirculation Flow Malfunction". I believe I either have to clean the EGR valve with carbon cleaner or replace the EGR valve all together. I am not sure which one is a better idea. In addition, I am not sure where is the EGR valve located and whether it can be replaced easily. Please advise. Thanks.

P.S. I had reset the ECU several times and everytime, it returned with the same trouble code after driving for about 45 miles. I think I have to do something about it before I take the car for state inspection. Thanks.

Best Regards,
William