I was driving the interstate recently, going between 65 and 70 MPH and my check engine light came on. So, I went to O'Reilly's and had them pull the code. It's a P0401 - Exhaust Gas Recirculation Flow Insufficient code. A couple of days ago, I swapped out the Cat and pipes from the exhaust manifold back to the flange for the muffler. I also put in a new gasket. Having done that, I noticed a certain sound as I accelerate; it sounds like air being forced out of the system somewhere--a leak, maybe. That's what I suspect the problem is with the code, but I want other's opinions on this. What else would cause this code? I'm driving a 2001 XLT regular cab 2.5L Lima. Help, please?

 

The EGR system uses the DPFE sensor to detect the amount of exhaust that is flowing into the intake via the EGR Valve when computer opens it

P0401 means DPFE sensor is showing a lower flow than the computer wants

DPFE sensor is a pressure differential sensor, it has 2 hoses that run to the EGR tube(metal tube from exhaust manifold to EGR valve)

One hose is close to EGR valve
One hose is farther away from EGR valve
When computer opens EGR valve the pressure difference between the 2 hoses is what the DPFE sends to computer, P0401 means there is not a big enough difference

Since both of these hose have exhaust gases in them they can fill with water(exhaust has lots of water vapor in it, it's why water drips from tail pipes and exhaust systems rust from the inside out, lol), and hoses get plugged up
They can also crack so leak pressure

Check the hoses, there is an order, so don't reverse them

The DPFE sensor can also fail, because of the water vapor they can and do fail

 

So, you think it has nothing to do with the catalytic converter? It's odd that I replace it and the light comes on.

Also, I was changing spark plugs a couple of weeks ago and got "unplug crazy" and unplugged the harness to the DPFE sensor but forgot to plug it back in until I had already driven the truck. This caused a check engine light, but I quickly found the unplugged harness and plugged it back in.

I removed the negative battery terminal for a few minutes to reset the light. That seems to have worked.

Could that have anything to do with the P0401 code?

By the way, I have another code which is going in a new thread. A P1000. I think it has something to do with resetting the light by disconnecting the negative battery terminal.

 

RonD, let me explain a little more because I want to nail down this check engine light issue. Here's what happened, in order:

1. Unplug DPFE and forget to plug it back in. Drive truck some, check engine light comes on, realize what I've done
2. Plug DPFE harness back in, disconnect negative battery terminal for 5 minutes and check engine light turns off
3. Replace cat, immediately when I drive I hear a "brushing" ("psshhh") sound whenever I accelerate from this point on (even to this day)
4. approximately 20 - 30 miles later, diving at interstate speeds (65+), the check engine light comes on with a P0401 code

That's where I'm at today. Before I jump to the conclusion that I have a bad DPFE sensor, could it be something with the changing of the cat and that escaping air/"brushing" sound I hear?
This site says an exhaust gas leak could throw the code. The truck never made that "brushing" sound as I accelerate until I had the cat changed. A shop did it because the bolts at the exhaust manifold were rusted on and I didn't have the tools to disconnect it. The shop tried tools, heat and eventually resorted to drilling out the bolts.

What do you think, RonD? Where should I begin? I want the truck to be right, you know?

 

An exhaust leak at the EGR manifold, tube or valve could certainly set an EGR code, but not a leak at the Cat

I would try to track down that leak, have someone hold rag over tail pipe while you listen to exhaust system to localize the leak

Moisture is what kills the DPFE sensors, all exhaust has water vapor, that's what happens when you burn a hydrocarbon(H) with Oxygen(O) you get some H2O
If you add high humidity in the air that is being sucked into the engine then you get even more H2O in the exhaust
This is why tail pipes drip water and why exhaust systems rust from the inside out

The DPFE sensor is mounted on the engine but it will still cool off faster than the rest of the engine so water vapor inside the rubber hoses and DPFE will condense, over time this will ruin the sensor
Most likely cause of the code is DPFE sensor failure, but certainly not the only cause

 

Where's the EGR manifold? Is that the exhaust manifold? Because that's where the cat bolted up. That's where the old bolts has rustem in place and why I had to take it to a shop.

Also, I replaced both O2 sensors; could that be a problem?

 

Yes, the exhaust manifold that EGR tube is connected to.....................

OOPS sorry, I see you have a 4cyl so just one exhaust manifold, V6/V8 engines have 2 so EGR tube is just on one side or the other

So yes if exhaust pressure leak is near EGR tube then it could cause that code

It will also cause Rich running because O2 shows false Lean to computer

 

I don't think that was ever tampered with. A tube running from the exhaust manifold to the DPFE sensor, right? Sorry to be dense. Obviously I'm not very car/truck knowledgeable, but I want to learn.

I'll check it though. Who knows what these guys did in their efforts to disconnect the cat from the manifold. Maybe they nicked the tube? I'll check...

But, you say the meeting of the cat with the muffler wouldn't cause the code?

 

Okay. The EGR tube is the tube running from the manifold to the EGR sensor (?--the saucer shaped component bolted to the intake manifold)? The tube is metal, right? Tapped into that is the DPFE sensor.

Yes, I think I'm tracking now. The EGR tube is bolted up solid. There appears to be no leaks at the DPFE sensor tubes. HOWEVER, I did loosen an EGR sensor (??) bolt, which subsequently stripped. I need to take it out and replace it. Could that cause the issue?

 

Yes, metal EGR tube runs from exhaust manifold to EGR valve on intake
Yes, it should have TWO hoses to DPFE sensor

Loose EGR Valve bolt wouldn't cause that code, could cause vacuum leak in intake

Yes, any time you have steel bolts going into an aluminum part, like intake manifold, or head, you have to be careful, steel is MUCH HARDER so will strip the aluminum threads if cross threaded or over tightened

 

Okay, I'm learning. The EGR valve connects to the intake manifold. I replaced the bolt and tightened it by hand, nothing more. But you say that shouldn't cause the issue, so I'm guessing no dice with the light.

Yes, the DPFE sensor has two hoses that connect to it, both of which connect up to the metal hose running from the exhaust manifold to the EGR valve. Those DPFE rubber hoses seem good; no obvious leaks. Pliable yet firm. The EGR tube is bolted tight to the exhaust manifold, but the nut looks new. i.e. no rust. The nut on the intake side is rusted bad.

Now you say a cat exhaust leak wouldn't cause this code--the manifold connection and muffler connection?The manifold side has no gasket, the muffler side does. Normal?

What's the best way to check the EGR tube? Take it off and look? DPFE sensor could be bad too. I don't want to replace **** I don't need to. EGR valve could be bad too? Again I don't want to replace it if I don't need to. How can I test these parts?

Sorry for the 1,000,000 questions. You are the most knowledgeable guy I talk to, plus you respond. Others here may be knowledgeable but don't respond to posts.

 

Okay, I've been working Google. A P0401 means the DPFE voltage is not consistent with a "ideal" stored value. This means the EGR flow is insufficient, which is checked in the EGR valve. So the most likely culprit in this case would be the EGR valve. I guess the new Cat I replaced, which is diffferent than the one that came off, exacerbated an issue with the EGR valve? Either way, I'm already pricing a new valve and while I'm at it I may as well replace the EGR hose too. Pricing that.

 

Get a piece of Vacuum hose from parts store, like 3 or 4ft, that fits the EGR Valves port, probably 4/16(1/4") or 5/16

Start engine let it idle
Pull off vehicles vacuum hose from EGR, put your vacuum hose on EGR
Suck on the end of your vacuum hose, i.e. apply vacuum to EGR valve, it should open and engine should start to run rough, suck harder and engine should stall, if so EGR Valve is OK

This vacuum hose can be use to repair/replace broke vacuum hoses down the road so not a waste of money

 

I've done more reading, RonD

How can I test the DPFE sensor? I read that that is the most common cause of the P0401 code on Fords, and the first thing to check. I'll start there.

By the way, thanks for hanging in there with me throughout this thread.

One more question: let's say it is the DPFE sensor and I replace it, is it okay to clear the light by disconnecting the battery for 5 or 10 minutes? Or should I have an OBD computer reset the computer in my truck?

 

Yes, DPFE sensors do fail and that is often the code when they do

EGR is an emissions system and you can't really clear an emission code with any method, CEL will go off on a reset or unhooking battery, but code will still be there and will come back if problem is seen again
Outside of the Misfire CEL(flashing CEL) computer won't turn on the CEL the first time it sees a problem, problem must be repeated a few times before it turns on the CEL
How many times is up to programmers of the computers, thats what Memory codes are for, so computer can see if same problem occurred before and how many times

Disconnecting the battery will make the computer run all emissions testing again, which is fine, up to you

Best methods to get it to run all the needed tests here: Ford Motor Company Driving Cycle
#8 is the one you want to do

EVAP system codes are the hardest to clear since there is no way to force a test of that system and it needs to pass tests a few times before memory code will clear itself

I wouldn't unhook battery and just let the computer clear the P0401 over the next few drive cycles assuming problem was fixed

 

Okay. I didn't know the CEL would turn off on it's own. So it needs to run it's own tests several times before it clears the code from memory (and then the CEL will turn off, right?)

I could disconnect battery to turn off CEL, do some normal driving to let it run it's own tests, and light will come back on if problem isn't fixed, but stay off if it is fixed by replacing DPFE and after a couple weeks of driving it should be cleared from memory, right?

Thanks for the link to the driving cycle but that looks tough to complete correctly. I'd prefer normal driving--it may take longer, but it's easier.

 

Yes, all correct

 

Thanks Ron! I went to my local autoparts store and bought a DFPE sensor (which is plastic, whereas the old one is metal--they wrote about it in the sheet that comes with the sensor) with a lifetime warranty, so hopefully that is the problem. $80 versus $55 online. But I want to get this fixed (hopefully).

Now I'm just waiting for my engine to cool down enough to handle the parts...

 

I took my old metal one apart, it was corroded past the seals and the circuit board was compromised with with condensation and rust.

 

Yes, the plastic ones seem to last longer

But the metal ones came in 2 versions, .55v and 1volt, have a read here: http://www.tomco-inc.com/Tech_Tips/ttt36.pdf

Plastic are all 1v models and usually 1995 and later will use 1volt so you should be good for 2001

And I think all Rangers used 1volt DPFE but not sure, Rangers used a position sensor on the EGR valve instead of a DPFE sensor into the early 1990's

The position sensors couldn't adjust for EGR valve and tube getting plugged up with carbon which limits flow of exhaust gases into intake so emission wise they were not reliable
DPFE pressure sensors actually measure the flow, so better for emissions end of things

 

I think I'll do the same. Kind of reassure myself that I just spent $80 wisely. Hopefully I did...

Yes, I read something about the voltages on the documentation that came with the sensor. It said that even if my truck uses 0.55V, this 1V sensor will be fine, only throwing a warning with the KOEO system. It won't effect the OBD II codes. Ford made a tolerance for it.

But, you say that my Ranger uses 1V anyway, so yay. Bonus.

 

I got my sensor direct from the Mazda dealer, it was not expensive at less then 40 bucks _ go figure.
Ford wanted at least double that for essentially the same part.

 

Well, I quickly decided I don't want to take apart the old DPFE. Drilling out rivets doesn't seem to be a good use of time to me right now...

But, I drove the vehicle some today, after disconnecting the battery, and no light. I know it still needs time to really run it's self-tests, but it's positive so far.

 

Well I guess I'm more curios then you.
I usually have fun tearing into stuff like that knowing that it's just had the biscuit anyway.
99% of the time drilling rivets out is a careful and tedious job, but in this case I just went at it on the drill press.

Don't chuck yours in the garbage though, you may find time later.

 

Do your husbands also work on cars...........................???

drill...drill press??............HAMMER or BIGGER HAMMER, and have a look inside


LOL, just kidding............well mostly