I have a 99 F250 LD w/ the 5.4 and I started getting the code P0401. Referred to this site and first sprayed throttle body cleaner everywhere....no luck. Replaced the dpfe sensor and was good for about a week. Went back and replaced the EGR and was good for about 3 days and back on. Any further suggestions would be helpful.

 

You need to remove the elbow between the throttle body and lower intake and clean the EGR passage in it. It will likely be plugged solid with carbon.

 

Check for broken vacuum lines between the battery and the firewall.. Thats what caused the 401 on my 5.4

The clogged egr ports are more common on the 4.6 than on the 5.4's

A quick check is to pull the Vacuum plug off the EGR control relay and with the motor running , use your finger to check for suction on the supply line. There should be enough force there to firmly hold your finger and raise a little red bump. If you just barely feel it then you know you are on the right track.. You could use a vacuum guage, but wheres the fun in that.

 

is the EGR control relay the same as the sensor? where is it located? I've had the same problem with the 401 code and replaced the sensor yesterday. it was more than 50% clogged. but the light came back on today???

My inspection is due and I can't get it inspected with a check engine light on???

I'm sure if the sensor was clogged so is the control relay...assuming they are not the same part.

 

If you follow the little vacuum line from the EGR valve it will lead you to the EGR control relay.

The sensor is different , DPFE , it has two rubber/silicone hoses that connect to the metal pipe that hooks between the exhaust pipe and the EGR valve.. This sensor tells the computer how much exhaust gas the EGR valve is letting flow into the engine. The computer then uses the control valve/relay to vary the vacuum supplyed to the EGR valve.

This gives you four components working in harmony, egr valve , control relay, DPFE sensor and computer, to make the EGR system function.. Any one of these along with vacuum supply, electrical wiring or exhaust gas port blockage, can conspire to cause the 401 code.

A quick check for proper EGR valve operation and port blockage is to disconnect the vac line from the EGR , connect a piece of line to the EGR and then suck on it like a milkshake.. With the engine idling , this action should cause the engine to stall.

 

Well I've even gone and removed my throttle body and cleaned it completely. It was pretty dirty so after I slapped it back on I cleared the codes and all was good and I was proud of myself......for about a week then P0401 again! So from the past post maybe I should try the relay??? WTF! Is there anything else it could be except that Egr control relay 864lightning was talking about?