I'm seeing two conflicting diagnostic codes on my 1997 Ford Contour: P0401 (EGR flow insufficient) and P0402 (EGR flow excessive). According to my OBD2 scanner, these codes appear contradictory. I'm trying to avoid spending $75 on a new EGR valve—does anyone have advice on what's actually causing this? Thanks for any insight.
I'm just trying to understand if the P0401 and P0402 codes are truly contradictory. I've only had my scanner for about two months and don't have regular access to a computer system. I haven't gone through all 111 pages of forum posts yet, and I'm not very familiar with this site—my apologies if I'm causing any inconvenience. Just need a bit of clarification here.
You're not putting me out at all—just mentioning that P0401 is one of the most commonly searched codes for Ford vehicles makes sense. There are already hundreds of posts and articles on this topic. Try searching 'P0401' directly in the forum—you'll likely find detailed discussions from owners of 97-00 Fords with similar issues. The EGR valve is rarely the root cause of these faults in older Ford models. When a DPFE sensor fails intermittently, it can register one moment that EGR flow is excessive (as if the valve is stuck open) and the next moment that flow is insufficient—this creates conflicting codes. While this isn't how a vacuum diaphragm EGR valve typically fails, it's similar to how a pressure sensor like the DPFE behaves when failing. A DPFE is essentially a more advanced version of a MAP sensor—it measures both pressure and vacuum instead of just vacuum or its absence.
Well then don't spend 75 dollars on an egr. Take the times to read the forums, look up what a dpfe sensor does and it may make more sense how you can get what you think are contradicting codes. Pretty common failure on all fords, beeen covered here 100's of times.