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How to: Diagnosing DPFE Sensor (P0401 and P0402) with Scan Tool

PapiBigRed

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04 v6 egr

Am I totally insane or is the the EGR and DPFE all one piece on an '04? Is there a way to test the DPFE?
 



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traveler

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Ok, I know this is an old thread but I didn't see the answer I needed. I've replaced the DPFE, and the code is back in less than a week. So what is the most likely next candidate? The EGR valve itself? Really need to get this code gone as I'm moving to a state that requires a test before getting a tag. Good Ol' Kansas doesn't care if its throwing a code, smoke, noxious fumes, whatever, so long as the car isn't listed as stolen and you have insurance, you're good. lol
 






Turdle

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copied from this link

http://www.samarins.com/diagnose/p0401.html


"One of the common problems with many Ford vehicles that can cause the trouble code P0401 is a bad or damaged DPFE sensor (DPFE stands for Delta Pressure Feedback EGR). When diagnosing the code P0401 on a Ford vehicle, the DPFE sensor and the hoses to the DPFE sensor are usually tested first. The DPFE sensor and its hoses should hold the vacuum; the hoses should not be cracked or restricted. The sensor signal voltage should change when the vacuum is applied. Sometimes the DPFE sensor hoses could be reversed during a repair and this also could cause the code P0401. Often, replacing the DPFE sensor with an updated part could solve the problem, however, other components of the EGR system also need to be checked. This thread shows EGR system components in the 2.3L Ford Ranger.
- The EGR valve could be sticking or the EGR passages could be restricted; both issues are very common. The EGR ports in the throttle body clog up very often too. If you are replacing the DPFE sensor, make sure the hoses are installed correctly and not crossed"

My suggestions.

Make sure the hoses are not blown out. They will often split or blow out near the connection to the dpfe. They can also blow off after heavy acceleration. If so, there might be a low flowing cat.

An exhaust leak on the passenger side will cause a p0401 due to the escaping exhaust pressure. The DPFE reads a differential of pressure between the 2 hoses so any leak will cause a lower reading there. (thinking of the broken bolts on the manifold ----)
 






traveler

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I'll double check for an exhaust leak, though I haven't heard one I suppose there could be one small enough to be masked by the louder muffler and tire noise. Also will check the hoses, though when I replaced the DPFE sensor they seemed to be in good shape, still pliable, not brittle, etc.

Off topic, the need to get to KSrocks in June just increased ten fold. The house has sold and closing is June 30th. So i'll be loading up a U-Haul on the 29th, signing papers the morning of the 30th and driving to AZ the same day!
 






Mainman407

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Btexpress;
While this DPFE discussion probably old hat, I have been experiencing a similar issue on my 96 Explorer XLT. Some time ago I had my EGR valve replaced. I think they also replaced the EGR valve regulator as well. Anyway, after installing the new EGR valve my vehicle ran rougher than a cob; I barely made it home. The next day I drove back to this shop and told them to replace the new EGR valve with the one they removed only to discover that the "new" EGR had a defect. Well about two years later after constantly being reminded by the 'Check Engine" light I decided to replace the old EGR valve. After installing the new EGR valve and checking the vacuum with a vacuum gauge to make sure the diaphragm was working properly, I cleared the P0401 DT code only to have it return 5 to 10 minutes later. I checked for any vacuum leaks but found none. The next culprit was the DPFE sensor. My DPFE sensor is nothing like the one in your photo. My DPFE sensor has two vacuum ports, so I tested each of the vacuum lines with a vacuum gauge All I saw on the gauge was some fluttering. In other words, no vacuum was reflected; and that was on both vacuum lines. I had REF voltage on the DPFE connector, however.

My understanding was that the DPFE sensor sends a pulse to the EGR valve and tells the EGR valve to open or close.
So, with no vacuum being shown from either of the DPFE vacuum lines, could this indicate that the DPFE sensor is bad?


"ExplorerDMB, post: 1491458, member: 22915"]Fords have an issue with their (Differential Pressure Feedback Exhaust Gas Recirculation [EGR]) DPFE Sensors. The DPFE sensor regulates how much exhaust runs back into the system for emissions reasoning.

Now, this is what it looks like:

dpfe-electronic-unit.jpg


If you notice the sensor above it is metal/aluminum. Now metal is a good conductor for heat, so when hot exhaust gas is passed through it, it eventually messes up the insides. This is why a DPFE issue is so frequent.

Ford tried to fix the issue with a plastic DPFE:

DPFE_Plastic.jpg


They last just as long as the metal ones. The voltage for the sensor (which can be found under Live Data or Data Stream in a scan tool) should be around .55-1 volt at idle. Anything higher and it should be replaced.

If you can graph out engine vaccum and the voltages you're likely to see, it would look similar to this graph:

DPFE_Voltage_Graphs.jpg

courtesy of rockledge

The most frequent codes with a DPFE sensor issue is a P0401 and/or a P0402. These mean following:

P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected


Now with the scan tool (I used a NGS on my last DPFE situation on a '01 Ranger 3.0L) you can verify your voltage at idle. The voltage I had was a little over 2 volts at idle. And I had the two above codes in the system - with only the 402 code coming on with KOER, but the P0401 was in continous/current codes.

If you unplug the sensor and the voltage reads 5.0 volts - then this means that your circuitry is good and that a sensor is needed.

Hopefully that helps some people. :thumbsup:


-Drew[/QUOTE]
 






Mainman407

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Traveler;
My symptoms are almost identical to what you have described in your post. My DPFE is plastic, and if my memory serves me correctly I replaced it as well. when I was experiencing issues with what I thought to be the MAP Sensor. While I did not replace the EGR valve at that time but I did erase the DTC P0401 code only to have it return moments later. Now I have two DTC codes; P0401 (EGR issue), and now P0402. According to information found on the Internet, the P0402 code was related to the Oxygen Sensor located on bank 1.

Oddly enough, I did finally change out the EGR valve and checked it with a vacuum pump to make sure the diaphragm was working properly, cleared the P0401 code, thinking everything was OK. Yet, again, the Check Engine light came on again.

One other thing, months ago, I just happened to notice that my odometer was not registering the mileage. After researching the issue I was told the problem was more than likely the Vehicle Speed Sensor (VSS). After replacing the VSS sensor located on the transmission rear housing appeared to be working afterward. Yet just the other day I happen to notice the odometer wasn't working again. I thought about
the sensor located on the rear axle gear housing. Do you have any suggestions what is causing this problem?

I don't want to bother you with some issues I am experiencing but I can't seem to find the POST THREAD button. One moderator said this POST THREAD box would be to the right on any forum topic. Well, I may be dummer than dirt, but I CANNOT find this button. Can you possibly help me?
 






guykickinit

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Bringing back an old topic. My 94 XLT would like a new DPFE every 6 months. (according to the mechanic I had to at) The shops scanner said it was the culprit. They said it went bad because of the acetone I added to the tank. I stopped doing that and it still went bad. I do have an exhaust leak in the muffler itself, and there is always water coming from the tailpipe. Thanks to ethanol gas.
I got an OBD2 scanner for my 08 Truck, and it's great. Anyone use one with an OBD1 pigtail. will it read their pre 96 vehicles?
Is there a way to bypass the DPFE? Our humidity is usually low. Right now it's 12%. I live in a desert.
Explorer works fine. no abnormal function. Accelerates great idles great. Just the pesky Eng light comes on after about 5 minutes.
 






~X~

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I've been getting a check engine light on my 94 for about a month. A scan showed EGR codes & I suspected the DPFE even though the part is less than a year old.

I put about 100 miles on the Explorer yesterday with intermittent cel the whole time. After reading this thread I decided to pull the DPFE and check for water and found quite a bit. I dried it out and reinstalled. No cel yet & I'll be putting another 100 miles on it today.
 






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87 Miles today, check engine light on and off the whole time. Cleared codes before I left, I'll check them again tomorrow & check the DPFE for water.
 






BrooklynBay

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guykickinit

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what would happen if the two hoses were disconnected from the dpfe and connected to each either?
Or would it be be better to add acetone to the fuel to dissolve the water?
 






BrooklynBay

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guykickinit

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I put in a specific amount for about 9 years on the coast and never had an engine light until I came out here to the desert. The acetone should burn off during combustion. It was only a few ounces per tank. I know most plastics dont like it. But I've gone through several sensors in the last few years. I stopped replacing it cuz it made no effect on operation. I think I'll try bypassing it.
 






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