Getting a P0401 trouble code, where I do look first?

One suggestion would be that the intake passages have a large amount of carbon build up. This would restrict egr flow and set an "insufficient air flow" code. Three possible fixes: 1. Use a high quality fuel system cleaner for the next 3-4 tanks of fuel, that may help to clean out the carbon deposits. 2. Remove the egr valve and try to run very small wire brushes into the intake to remove the carbon. One draw back to this is that carbon pieces will become dislodged and may cause a valve to stick. 3. Remove the intake and have it hot tanked at an engine rebuilding shop.

Are you sure that it doesn't have a differential psi. sensor in-line with the EGR. I am not saying your not right just double check it

because I have ran into this before it is simply a sensor with two different size lines on it and ford has had many go bad. Follow the line coming off your EGR valve and see if it runs into a sensor that haves a different size line on the other side. It also could be a pin hole in one of your vacuum hoses or it could be any of the other suggestions from the previous answer. P0401 is EGR insufficient flow as you know, the only thing that detects flow is an EGR sensor that actually measures the Mechanical movement of the EGR or the Differential PSI. So if you don't have the DPS then you have a EGR position sensor mounted on top of your EGR valve if there is nothing mounted above your EGR then you should have the Differential PSI sensor so just look over everything good. GOOD LUCK

if u replaced the egr valve and u still getting a code after u clear the code, check ur vacuum lines.make sure they all on correct fittings. follow each line leading to and from ur egr valve to their stopping point. u could have a pin size hole anywhere or a crack. yes u need to wire brush the tubing running to the egr valve. u can use some intake cleaner and spray the tubing opening and inside as much as u can get. yes u do have a dpfe sensor or a pfe sensor. that is what tells ur pcm that the flow is insufficient.

4.8L?-I think you mean 4.6L which does have a DPFE. But the problem is very likely that the throttle body EGR passage is plugged full of carbon. Simple to test, just apply vacuum to the EGR valve with a hand vac pump while eng is running. If engine stalls or sputters this is not the problem, but if there is no change then there is no EGR flow through the throttle body or valve.

http://www.mycarstats.com/

http://www-odi.nhtsa.dot.gov/cars/problems/tsb/tsb...

http://www.edmunds.com/maintenance/MaintenanceServ...