Originally posted by F111D F:
I thought your clog was the EGR passage on the upper intake manifold?
Actually, I ended up replacing most of the major components on the EGR system!
I originally took the the EGR valve off and cleaned it with TB cleaner, but the P0401 came back on.
I decided to replace the EGR valve and found that it was clogged up, even though the valve was opening and closing properly under vacuum. As I said in my previous message (above), I shone a flashlight in one end (when the valve was open) and there was no light coming out the other end. This showed me that even though the valve was opening and closing, it was clogged for all practical purposes. To verify my results, I tried the same test on the new EGR valve and you could see light come out the other end. I reset the CEL, but the P0401 came back on.
I then tested the EVR (with Alex Peper's Vehicle Explorer) and found that it was giving erratic readings, so I replaced it. I reset the CEL, but the P0401 came back on.
I then tested the DPFE (also with Alex Peper's Vehicle Explorer) and found that it was also giving bad readings, so I replaced it. I reset the CEL, but the P0401 came back on.
I finally found that the EGR passages on the UIM (behind the TB gasket) were totally clogged and cleaned them. I reset the CEL, and the P0401 never came back on! Problem solved. Drove to New York City and back over the weekend (over 800 miles) for a wedding. Still no P0401. Halleluhah!
