I have a 2002 f-150 with a 4.2L 6 cyl. motor standard ,my service engine soon light keeps coming on.I used a scanner and the code po 401 comes up saying egr flow insufficient I have had my truck to the service shop 3 times for inspection it will not pass with the light on. I have had the egr valve replaced now 2 times and it still comes back on .Any help would be greatly appreciated. Thank You

 

I would check the vaccum lines. if its like mine than it has vaccum line going to it on the top witch controls it. I would do that first. If that doesnt work try disconnecting your battery for a while to reset the computer, put it back on, drive it for about 2-3 days, than if light doesnt come on by then take it to get inspected!

 

When the valve was replaced, was the passages cleaned out also? If carbon is in the passages it will cause the code to come up. The DPFE sensor will also cause that code.