I have literally replaced all the sensors clean the throttle body clean the Cadillac converter tried vacuum tests change fuel filter air filter MAF sensor DPF sensor all the sensors involved truck is now starting to stall while breaking hard and hesitating while accelerating only while in gear when in park idles fine. Tired of throwing time and money at it if anybody has any suggestions they would be great!! Code still persists. Been fighting this over a year. Please any idea ?

 

P0401. Have you checked and cleaned the EGR valve that may be slightly stuck open? If there is a carbon chip holding it slightly open sometimes it can be cleared without removing the valve. Use a hand vacuum pump and open the valve to maximum. The chip may dislodge. If not remove valve and check for carbon and operation.

 

Yes I’ve cleaned the old one and code came back I had a warranty on it so I figured to just replace it so I was sure it was good, cleaned the entire throttle body and all the hoses checked for leaks , replaced the all the sensors, the egr sensor I’ve replaced 3 times just to be sure. Truly at a loss on what to do been doing research other forums and everything any one has suggested I’ve done several times just to be sure 100% and it goes away for a couple days then kicks right back on.

 

This a v10, so there are two egr temp. sensors right ? Were both replaced ?

 

Everything related, even went as far as cleaning the cat converter and fuel filters and fuel regulator about to do intake manifold gaskets.

 

You may need to take it to someone with a high-end diagnostic scanner to monitor the signals and see what is going on....

 

P0401 is low EGR flow
The port to or in the throttle plate might be plugged up like the 4.6's do
I would pull the throttle plate and inspect the port

 

The auto parts store EGR sensor is not like FORD ones. The Ford one is about two or three grams heavier than the ones you get there. (Ford one is around $125.00 and auto parts one $35.00)
Seen the Ford one fix a lot of engines where this code and its sister code would pop up.

 

I paid 90$ for the part .. changed 3 times

 

ScannerDanner has some Ford P0401 videos on YouTube that may be helpfull..

 

The code 401 tells you the EGR is not opening = low flow on the self-test and sets the code.
You done all the other things that had nothing to do with the Code for low flow.
The EGR is requested to open by the computer opening the Vacuum control line to the EGR and letting engine vacuum pass to the EGR.
The test is done at startup 2 times to be sure there is no moisture/ice in the lines blocking the vacuum signal during freezing temps.
Is the EGR Control solenoid working, blocked stuck closed, it's filter dirty etc.?
Take it off and test it for this function and check the filter under the round cap. It is a 3 port device. One in, One out and one to relieve the vacuum in the EGR to the outside when the EGR is not called to function.
Test the EGR for holding vacuum using a hand vac pump. If you do this with the motor at Idle, the motor e will stumble indicating the port into the intake is open/un-blocked, as it should be.
The only time the EGR is opened is at start up and during the drive cycle above about 45 mph, otherwise you cannot make it open by racing the engine throttle.
Make sure the DPFE is electrically plugged up and the hose assignments are correct to the metal line between the exhaust manifold and the EGR VALVE. There are two hoses because they are on different sides of a internal restriction hole in the metal line so the DPFE can make the flow measurements and report them to the computer.
Let everything else alone. and hope you did not introduce another issue to cause confusion.

 

P0401 is low flow not EGR valve not opening
Most of the time it is just a plugged port. melted hoses or the DPFE is no good
Simply follow the pinpoint tests in the H manual for code P0401
If you have no test equipment remove the valve and check /clean the ports