I'm having trouble nailing down a P0401 CEL. At first it seemed that the DPFE sensor was bad (metal one) based on input from the dealer. I replaced the DPFE with another metal one, then reset the computer. The CEL came back on within 25 miles. I then found this web site and some related info. I pulled the throttle body off and found both EGR ports totally blocked, I cleaned those, reset the computer and sure enough within 25 miles the CEL came back on. At this point I can apply vacumm to the EGR valve and the engine stalls. I put the old DPFE sensor back on and applying vacuum to the EGR port still stalls the engine. Anyone have any suggestions?? Thanks!!

 

About the only thing left is the Egr Vacuum Regulator.

Any leaks in the vacuum hoses?

Vacuum hoses plugged up?

 

Thanks, one thing I didn't think to check was that the CEL was the same P0401. I went to Schucks and had the code read. Now I'm getting P0171 and P0174 System to Lean (both banks). I reset the code using the code reader and I'll see if it comes back. I found some posts concerning the PCV vacuum line at the back of the throttle body. I'll check that out since I remember it was difficult to get out and put back, so I may have kinked it or not connected it all the way. Thanks!

 

Are you sure when yo0 put everything back together that you didnt pinch a gasket. I had problems with my 97. I cleaned and replaced everythng and still got a light. I got the lean code. Turns out I had pinched a gasket and created a vacum leak.

 

anyone heard of a "ANTI-KNOCK VALVE"? IHAVE A 1998 WHITE F150 W/103K mi, and the CEL comes on, on old timer mentioned this "anti-knock valve". would it help? codes have been PO171, PO172, PO401 & PO174
Thanks

 

i just got back from the dealer and he went over the truck with a vaccum gauge, diagnostic computer, and a flashlight. turns out the problem area for me was on the passenger side there was a line loose near the #1 & #2 cylinder. he said it was prolly bumped when i changed the plugs/ wires. he also used a drill and long cleaner attachment to clear out my EGR tubes. the DPFE sensor and the valve in front of it checked out, the EGR diaphram also checked out, but for some reason the EGR had no vaccum pressure (as stated above somethign got knocked loose).