Engine Light "code P401 insufficient air flow



I have a 1996 Ford Explorer XLT with 130,000 miles, runs great but engine light is on, code is P401 insufficient air flow, I have replaced the EGR valve and EGR pipe, sensor and solenoid, all vacuum lines are good and have disconnected battery overnight to reset but engine light comes back on at about 30 miles, I even put one of the lines back wrong and the truck ran terrible. I have no clue what to do next, I cannot get a sticker until I fix this problem.




Stop a block from the test center, reset the light, get the test…

Is the code “EGR low flow” or what?


Make sure all the egr passages are clean with no carbon or anything clogging them up. Also make sure you are getting a voltage change when you apply vacuum to your differential pressure feedback electronic sensor, or DPFE sensor for short.


Possibly, the catalyst is plugging up.


This in-depth article could contain the solution you need: http://www.asashop.org/autoinc/dec97/egr.htm


I had the same problem in my 1996 Explorer Eddie Bauer with 4.0L engine. To make a long story short (EGR valve cleaning, DPSE switch, modulator solenoid valve, carbon cleaning, nothing worked) it turned out that when I replaced the rubber grommet-like seal on the end of the metal EGR pipe where it goes into the intake manifold plenum, the light went away (2-3 years ago). That’s apparently why the flow was insufficient. (The old rubber seal was kind of deformed). Take that pipe off and replace the seal ($10 at Ford). Good luck.