Persistent p0401

[cdxhizors]

I've done a lot of reading, replaced every egr part and still have the p0401

More detail, I've replaced the dpfe, hoses to the dpfe, egr line(big metal pipe), egr bung in the manifold, of course the egr. Checked the line that goes into the intake and it's clear. The vacuum lines to the egr are fine. What else can I do? The light stays off for hundreds of miles giving false hope lol. Truck runs great. Never feels different when the light comes on. Just decided to throw it randomly.

 

[RonD]

There are 3 parts to an EGR system
EGR valve
EGR Modulator(solenoid)
DPFE sensor

EGR modulator is controlled by the computer, it is a 12volt solenoid that passes vacuum to the EGR valve to open it.
Computer Pulses the 12volts to the solenoid to pass a little or alot of vacuum to the EGR Valve, so opening it a little or alot.
"Insufficient EGR flow" could mean solenoid is not passing enough vacuum to EGR valve to open it all the way or as much as needed.
The DPFE sensor tells computer how far open the EGR valve is by the pressure difference between the 2 hoses, computer adjusts 12volt pulses accordingly, so there may be enough vacuum to run engine under lighter loads fine, but under heavier loads when computer needs to open EGR valve fully there may not be, so P0401 wouldn't come up until then.
Fully open EGR system isn't used that much, EGR's purpose is to cool down cylinder temps to lower NOx emissions that spike when cylinder temps go up, accelerating and going up hills heats up cylinders.

You can test this solenoid with 9volt battery or the truck battery.
when voltage is applied it should "click" and open all the way.
It is a simple solenoid(coil of wire) so there is no +/- polarity, if one connector has + and the other - then solenoid should "click" open.
If you attach a hose to one port on the solenoid and then blow into the hose while solenoid is "open" there should be no restriction, should be the same as blowing thru the hose when it isn't attached to anything.
If you have a vacuum gauge then attach one port of solenoid to engine vacuum and the other port to vacuum gauge.
Start engine
When solenoid is "open" you should see 18-20" of vacuum, full intake vacuum being passed to vacuum gauge.

 

[cdxhizors]

There are 3 parts to an EGR system
EGR valve
EGR Modulator(solenoid)
DPFE sensor

EGR modulator is controlled by the computer, it is a 12volt solenoid that passes vacuum to the EGR valve to open it.
Computer Pulses the 12volts to the solenoid to pass a little or alot of vacuum to the EGR Valve, so opening it a little or alot.
"Insufficient EGR flow" could mean solenoid is not passing enough vacuum to EGR valve to open it all the way or as much as needed.
The DPFE sensor tells computer how far open the EGR valve is by the pressure difference between the 2 hoses, computer adjusts 12volt pulses accordingly, so there may be enough vacuum to run engine under lighter loads fine, but under heavier loads when computer needs to open EGR valve fully there may not be, so P0401 wouldn't come up until then.
Fully open EGR system isn't used that much, EGR's purpose is to cool down cylinder temps to lower NOx emissions that spike when cylinder temps go up, accelerating and going up hills heats up cylinders.

You can test this solenoid with 9volt battery or the truck battery.
when voltage is applied it should "click" and open all the way.
It is a simple solenoid(coil of wire) so there is no +/- polarity, if one connector has + and the other - then solenoid should "click" open.
If you attach a hose to one port on the solenoid and then blow into the hose while solenoid is "open" there should be no restriction, should be the same as blowing thru the hose when it isn't attached to anything.
If you have a vacuum gauge then attach one port of solenoid to engine vacuum and the other port to vacuum gauge.
Start engine
When solenoid is "open" you should see 18-20" of vacuum, full intake vacuum being passed to vacuum gauge.

Thank you, that's gotta be the last part of the system to replace. I'll try the tests but it has to be it unless it's computer related.

 

[cdxhizors]

So when the truck is off and key off I can barely blow through the solonoid. Same with key on. Possibly not working? I don't have access to some jumper wires to test it with direct battery voltage but I figured key on it should close it.

 

[adsm08]

The EGR solenoid is normally closed. This means when it has no power going through it there is also no air going through it. So key off it is close, and key on it is closed. It is only open when the computer requests EGR flow. So far it sounds like the solenoid is operating at it should. But you haven't tested it under the full range of conditions yet.

 

[RonD]

+1 ^^^

You need to give solenoid 12volts and measure or see what it's flow is.
As said EGR system isn't used all the time, only to prevent cylinder temps from getting too high.
So not really possible to do static test, i.e. in driveway testing, while it is in place.

 

[cdxhizors]

Well according to my test it leaks. Right? I can pass air through it with it off. I'll try applying 12 volts to it and see it if clicks and opens.