A while back my truck had code P0401, insufficient EGR flow. I cleaned the EGR valve, tube & all vacuum lines. I had no vacuum, Recently I got the same code. I followed the same steps as before. I now have vacuum but the truck loaps really bad with line connected to the EGR valve. If I disconnect the EGR valve vacuum line, the truck seems to idle a little better. Can anyone make any suggestions as to what could be causing this ?

 

Hi, and welcome to FTE and the 4.2/3.9 Forum.

There have been several posts here over the years regarding P0401 (and P0402) codes.

While in the 4.2 forum, Click on "Search this forum" the top and type "P0401" in the search box. You'll get plenty to read.

I seem to remember 2 most common causes:

bad DPFE sensor
or
clogged EGR ports

Best of luck with repairs and let us know what you find as the cause.