1998 Mercury Mystique Fault Codes P0404 and P0401: Diagnosis and Repair Steps

Model: 1998 Mercury Mystique Fault Code: P0401 Posted: 2014-05-24 19:42

I own a 1998 Mercury Mystique that recently triggered diagnostic trouble code P0404. I replaced both the EGR valve and the DPFE sensor, but the issue has now shifted to code P0401. What should I do next to resolve this problem? The vehicle is experiencing poor fuel efficiency and rough idle, which may be related to the exhaust system performance. Any insights into potential causes or troubleshooting steps for P0401 in a 1998 Mercury Mystique would be greatly appreciated.