I have a 2004 mitsubishi lancer and just recently got this code. I vacuum checked the egr valve and it seem,s to be working properly. Cleared the code and has come back again. Any suggestions on what to look at next?
Did you check the EGR vacuum control solenoid?
Tester
P0401, “EGR insufficient flow detected” tells you that: the EGR flow is less than it should be, or that the detection of flow report is erroneous. Your job: check the passages, to, through, and from the EGR valve for carbon buildup, and check if the other parts work.
It seems you may have the repair manual. That will help you bunches.
Try this link for suggestions: http://www.obd-codes.com/p0401 (basically, DPFE sensor, bad EGR valve, low vacuum, plugged EGR plumbing). But do read the link. There’s a generic test procedure there.
My experience has been that generic advice on problems like this most often works fine. However many cars have slight variations on the normal ways of doing things. When the engineers have done something different, about all you can do is puzzle out how your car is supposed to work and devise your own tests.