Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

My Check Engine light came on April 2002, over a year ago on my 1997 F150 with a 4.6L engine. I've had the codes read a number of times since and I cannot seem to rid the P0401 code. This code is listed as "EGR Insufficient Flow Detected".

I originally thought the problem was the DPFE sensor. This was replaced with an orignal Ford part. During a tune up, the connector broke on the EGR vacuum regulator so it was replaced -- again with a Ford part. Since the light was still on, I went ahead and replace the EGR valve (as this is the final component in the EGR system). Again, a Ford part was used.

So, I don't know what else to check. The only thing left that I can think of is the orifice in the EGR Pipe is clogged.

Anyone have any experience with this?

The truck has about 96K miles and runs great. It has no noticiable problems and had a recent tune up with all spark plugs and wires replaced. (Earlier I also had a P0304 -- Cylinder No. 4 misfire but that was fixed.)

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hi Al_Cuevas and welcome to FTE :)

I assume you cleared the code after you worked on it?
The DPFE sensor is by far the most common problem.
You could also have plugged EGR ports in the manifold.
If you apply vacuum to the EGR with the engine idling it should stall or almost stall if the EGR is flowing. If not you probably have plugged ports.
If you remove the EGR valve you should be able to see if they are plugged.
Let us know what you find.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hi Dave, thanks for the quick reply.

Yes, the codes were cleared after each repair (and even between repairs). I don't recall seeing any problems with the EGR ports. On the original EGR valve, it was not really that bad. That is, it did not have a lot of carbon build up.

I have not yet tried to apply vacuum to the EGR valve as you've suggested. I'll see if I can borrow a vacuum pump to do this.

When I originally checked the DPFE, I was not getting any voltage on the connector. It was a bit difficult to get a reliable reading as I needed to insert a wire from the backside to make the connection. I guess it is possible that I got a defective unit and I'll recheck the voltages again. If I remember correctly, I was not getting the VREF voltage.

Occassionally, the check engine light will go off on its own. This seems to happen on long trips of highway driving, say of about 60 or so miles. I know the computer will clear the code if it doesn't see the failure in 3 or more consecutive drive cycles.

I'll continue to look at the DPFE and will report back when I have more information. Hopefully, I can work on it in the next couple of weeks. Thanks again.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

First, let's talk about insufficient EGR. Such a defect is only noted because the vehicle won't meet emissions laws. The Feds want you to keep that system working properly. There is some relationship between the EGR calibration and the spark advance, but I doubt you would notice the interaction.

Second, you've hit all the trouble spots except the orifice and feedback sensor lines. The orifice is in between the two tiny pipes leading up to the DPFE sensor. I can't figure out how anyone would clean it! Maybe pull the pipe and run a pressure washer nozzle into one end? Would NOT want to be near the other end!

Third, the valve and plumbing may be totally fine. The code would be set based on the DPFE sensor alone, so either (1)there is no DPFE signal, or (2)there are leaks or disconnects in the pressure lines leading to the DPFE sensor and it thinks there is no flow.

Fourth, the valve will remain closed until the vehicle is moving. Hence, there will be "NO" feedback sensor voltage since there is no flow. There should be ground, supply, and signal wires on the sensor. But, you won't be able to accurately assess the sensor unless you put a high impedance voltmeter in parallel with the ground and the signal wire, and run these leads into the cab and drive. It is fun, but it is a bit of work. A lot of the time the signal bounces around and you can't really read what the computer would see because the multimeter can't follow the voltage fast enough. You could try an oscilloscope (battery powered) but even that is difficult to use. Usually takes a test driver and a data person.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Chipster I've noticed quite a few P0401s lately that there was a definate difference in the way it ran with the EGR working properly and giving a proper reading compared to not working properly. A lot of vehicles will surge quite bad at part throttle with no PFE reading due to the PCM not knowing to change the timing and A/F ratio to correspond to EGR flow.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Interesting! They must have really changed the calibration to minimize NOx at that part throttle condition. If the computer is keeping the fuel delivery higher due to the lack of EGR, and you can feel the extra power (surge) that is a lot of EGR they are calling for. Maybe what is happening is that the PCM thinks the EGR is there, reduces fuel to accomodate, sees LESS EGR than expected, boosts fuel to compensate, and the driver feels the surge. My memory is hazy, but I think the maximum EGR flow at 14 inches Hg is 20 cubic feet per minute.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

What they feel like on the ones I've driven lately is a lean surge.
I should monitor the fuel trims etc some time on one that is surging and see if i can pick up what is happening.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Chipster & Racerguy,

Thanks for the input. I wanted to let you know that I don't see any problem with surges. There's no loss of power or anything like that. As best I can tell, the fuel consumption appears to be normal. I get about 14 to 15 mpg in the city and that's what I've been getting since I got the truck.

On a very rare occassion, the truck will idle rough at a stop. This happens so rarely though. That's why I changed out the plugs and wires. BTW, all plugs were in really good shape at about 90K miles except #1. It was down to a nub, but the PCM must have been compensating for it (or I couldn't feel the effects).

I hope to check the DPFE this weekend. I see your point about checking while driving and maybe I can rig something up.

In the meantime, where does the VREF voltage originate? If I understand the operation of the DPFE, VREF is the input and VSIG is the output from the DPFE. The Haynes manual I have says VREF should be between 4 to 6 volts (ignition key ON, engine not running). It says with the engine running cold, I should measure 0.2 to 0.7 volts on the VSIG line. As the engine warms, it should get to 4 to 6 volts.

Is there any other way for me to test the DPFE off the truck?

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

VREF originates in the PCM.
At the DPFE sensor VREF is the Br/Wh wire, Signal Return (ground) is Gy/Rd and the PFE signal is Br/LG.
VREF should be 5V or there abouts.
At a hot idle your PFE should read usually just under 1V, with the EGR open it should read approx 4V if EGR is actually flowing.
I dont think there is any way to easily test the PFE off the truck.
I'd start by applying vacuum to the EGR and see if the idle changes....that way you'll know if the EGR is capable of flowing.
This is what the manual says about a P0401.............

Diagnostic Trouble Code (DTC) P0401 indicates that Continuous Memory Self-Test has detected insufficient EGR flow.

Possible causes:

Fault in vacuum supply to EGR vacuum regulator solenoid.
EGR valve stuck closed or iced.
EGR valve diaphragm leaks.
EGR valve or flow path restricted.
EGR vacuum hose off, plugged or leaks.
VPWR circuit open to EGR Vacuum Regulator solenoid.
EVR circuit to PCM open.
EVR circuit to PCM shorted to PWR.
Differential Pressure Feedback EGR (D.P.F. EGR) sensor pressure hoses both connected improperly.
D.P.F. EGR sensor pressure hoses reversed.
D.P.F. EGR sensor VREF circuit open.
Downstream pressure hose off.
Downstream pressure hose plugged.
Damaged orifice tube assembly.
Damaged EGR Vacuum Regulator solenoid.
Damaged D.P.F. EGR sensor.
Damaged PCM.

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

there is a tub that goes through the intake it gets clogged up take it to a shop and have them take the intake off an d clean it out it cost me $100

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hey this is my first time here ,I came to this site insearch of an answer to the same problem you are having. I havebeen fighting this code for 2 years now.I have tryed every dealership,garage around .I have tryed everything that I read from your responce,but that darn light will not stay off! driving me nutz! sorry this is on a 1997 F150 4.6 4x4 5speed :-X09

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hi woodysf150 and welcome to FTE :)
Have you removed the throttle body to check the ports in the intake manifold?

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hi Dave ,I have not pulled the intake up to this point i did check the ports behind the EGR valve and they were very clean so it led me to believe that they were ok. i have not had much exp. with newer vehicles but ido enjoy working on the older ones before all the electronics come into play! im just kind of stubern thought i could fix it .kind of funny i had to learn to use this darn thing to figger it out. I am going to pull the intake this weekend to look inside,clean out . Keep fingers X, Anyway thank you for your help. God i hope this does it, I will let you know how it goes.Dave is there any type of surprises I need to watch out for while attempting this?

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Hey Dave ,sorry i forgot to ask you if you know the proper torqe setting for the upper and the lower mannifold bolts? I dont use the computer that much kinda slow, Thanks

Code P0401 -- EGR insufficient flow, 1997 F150, 4.6L
 

Actually you dont have to remove the whole intake, just the throttle body. It's not a big deal to do that.
One thing you can try first though is to apply vacuum to the EGR valve with the engine idling. It should make it stall or close to stall if it is working. If not then you have a faulty EGR valve or the ports are plugged. If that test passes (engine stalls or almost stalls) then you are probably looking at an electronic problem.