Hey all, first post. I searched and read all I could on the 4.2 problems with 0401 and 0402 codes, let me give my symptoms:

2002 F150 2WD, 4.2L V6, Auto Trans, 74k miles, 90% highway driven.

I got the SES light about a month ago, and pulled a P0401 code (EGR flow insufficient) at AutoZone. I did some reading and found all kinds of hits on the DPFE. I did a manual vacuum test on the EGR valve at idle and it worked fine (engine stumbled when vacuum applied). I took the EGR valve off, inspected it, made sure it moves smoothly and "de-carboned" it as best I could. I did not see any blockage in the EGR port in the intake. I inspected the green vacuum line for breaks, etc. and it was fine. I called the dealer and they said the DPFE was the problem 9 out of 10 times. So, I bought the $37 Wells brand DPFE from AutoZone, reset the code, and all was well, for about 3 weeks...

Now, as of last Thursday, I have the SES light again, only this time I get P0402 (excessive EGR flow). After the reading I've done on here, I'm leaning toward replacing the DPFE again with a genuine Ford part. Does that sound about right? Is there anything else I missed that I might try? The only other part in the system is the vacuum solenoid that would turn the vacuum to the EGR valve on, correct? How to check it? Certain RPM and engine temp?

I have no driveability issues, mileage is still great, but I do seem to have a slight "buck" when I let off the throttle at highway speeds. Almost like the tranny clunks back into the engine braking.

Thanks in advance for any help.

 

Probably you have a bad DPFE. Wells parts have been of substandarded. Try either a Ford replacement or go to O'reillys or Advanced if you have them.