How to: - Diagnosing DPFE Sensor (P0401 and P0402) with Scan Tool | Ford Explorer Forums - Serious Explorations

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

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January 26, 2004
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City, State
Mechanicsville, Virginia
Year, Model & Trim Level
2004 Acura TL
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:


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:

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:

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:


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Nicely Done Drew.

In response to the post about DPFE sensor.
Being I work for the company that designed and manufactured the sensor for Ford Motor Corporation I cannot mention the company name. I think I need to add a few statements and clarify some problems here. I am a design and failure analysis engineer for this project that is no longer in production. As stated it is a differential pressure transducer that is designed to read the difference of pressure across the EGR valve opening. You have stated that “heat was the cause of the electrics failures” well that is not true the internal sensor and the electronic are made of ceramic and high temperature solder designed to work at temperature above 150C. The 1500C exhaust stream does not pass through this transducer the pressure applied to the sensor is a dead head so the thermal transfer is contained to the stagnant air trapped in the hoses to the sensor that is very slow to transfer heat. The real cause of the failures is water and trapper acids in the water. Ford did a poor job of preventing the build up of water in the EGR system which ended up corroding the inner seal glades of the transducer and allowing the water and acid to come in contact with the electronics as you a know water and electricity do not mix. The biggest cause of the failure was do to short trip driving which did not allow the water to be removed from the system and a build up would happen at a higher rate.
The graph that shows engine vacuum and sensor output voltages is not complete. Being this is a differential pressure transducer it is designed to read a pressure difference. Being there is a high and low pressure port if the pressure on both ports are equal the transducer will read .500 VDC but if the pressure is lower on the low pressure side the transducer will produce a linear increase in voltage. So if the EGR Valve opens the output goes higher 4.500 VDC Max because the pressure has changed and is lower. When the EGR valve is closed the output should return to the .500 VDC range because the pressure is equal again. I could go farther but that is the premise of how this transducer works on this system.
Now the second transducer plastic was a second source for these transducer and they had a higher failure rate then the Aluminum housed transducer. The plastic housing was to reduce cost of this transducer not to dissipate heat in fact the plastic transducer would melt with pressure leaks
The sensor has had a very good track record over the years there were over 4 million sensors produced a year for 5 years and the return rate was 10 parts per million which is pretty dam good being these transducer have to last at least 100000 miles without failure in a very nasty environment.

I'll admit to the nasty environment. I will only say that in my somewhat limited experience, anytime I had an EGR issue in a DPFE equipped vehicle, it was the DPFE that had failed. I have replaced a few in my day.

So does a 2000 5.0 Mounty have one of these and can it trigger a bogus failed O2 sensor?

You maybe right that you detected a fault in the DPFE sensor but in 70% of the returned product from Ford the transducers were functional and in operational ranges. Most of the automotive repairs are plug and play so when you replaced the sensor you drained the trapped water in the lines leading to the transducer like a finger covering the end of a drinking straw and the new sensor worked fine. We proved to ford on a test Dyno in our plant that the build up of water was causing fails readings in the transducer. If you looked at the new configuration this day and age the sensor does not see the full exhaust stream it only reads the pressure across a very small port in the EGR Valve no more trapped water.

Most likely No. Running rich or agian water on the sensor is a big cause have you noticed the water dripping from the tail pipe or Fords wonderful wiring harnesses shorting or open condition?

A check valve would make the problem worse you need a much larger ID tube before the Transducer so the water surface tension can not hold the water in place in the tubing.

Water trap sure if you can find one that can handle the heat and the acids Plus find the room to put it in. But the more volume you add to the system the slower the responce to pressure change which would slow down the computer responce time. The best thing to do is drain the lines every 50,000 mile or move some place with lower humidity .

Glacier991 said:
I'll admit to the nasty environment. I will only say that in my somewhat limited experience, anytime I had an EGR issue in a DPFE equipped vehicle, it was the DPFE that had failed. I have replaced a few in my day.

100% agree :thumbsup:

Whenever there is a EGR issue on a Ford in the shop - pretty much everyone runs to test the DPFE.


Where can I get a DPFE? I unplugged mine to see if our Mounty would run any better and it made a noticeable difference. I am searching online for one and haven't been able to find it.

If I plug both lines of the DPFE, what will happen? Is that a useful means to test because the second time I drove it today it ran horrible.
You can e-mail me offline or PM me regarding testing of the O2. Really need to get this thing fixed -and soon. Hopefully by the end of the week.

There you go !
Read the bottom of page 24 ! Water Vapor !

you can go to your local autozone and get a DPFE, it will be listed in their computer as an "EGR Valve Pressure Sensor".. i paid a whopping $39.99 (my wholesale i work at has an account)..compaired to fords wholesale price of $134.99.
Oreillys does not carry the DPFE.
and reguarding the Oxygen sensors, if you go to Oreilly's they are cheaper than autozone's. I ended up getting Both O2 sensors Bosch part # 51717--for the 1995 4.0 year model only-- for $91.45.. or like 45 each..

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