On my way home today my truck threw a check engine light. The confirmed trouble code is P1401, DPFE sensor circuit high voltage detected. The PCM module also showed that code and two more codes: P0402 EGR "A" Flow Excessive Detected and P1405 Plugged or Open upstream Hi side DPFE sensor. Haven't performed any further diagnostics yet, but any insight on where to start would be helpful. The truck has 223k miles on it, and has the original aluminum DPFE sensor which I read can be faulty. Also the truck does ping sometimes which I am assuming could possible have something to do with the EGR system not being 100%.

 

Yes, most common reason for those codes is that the DPFE sensor has failed in some way, because they do wear out from moisture intrusion.

The DPFE sensor works by having TWO exhaust hoses running to it from the EGR tube, these hoses can crack or break so should be looked at

Inside the EGR tube is an "orifice", plate with a hole in it

One of the DPFE hoses is farther away from EGR valve and on one side of the plate, the other hose is closer to the EGR valve and on the other side of the plate

As the computer opens the EGR valve the hose closer to the EGR valve has a pressure drop, the pressure difference between the two hoses is what the DPFE sensor reads and sends to the computer, so the computer knows how much exhaust is flowing thru the EGR valve and into the intake manifold.
DPFE = differential pressure feedback or delta pressure feedback


All exhaust has high water vapor in it, when you burn Hydrocarbons(H) with Oxygen(O) you get a by-product of H2O(water)
This is why exhaust systems rust from the inside out, lol, and why water drips from the tail pipe

So there is moisture in the DPFE hoses, because there is exhaust in the DPFE hoses, over the years that moisture can cause the DPFE sensor to fail


There may be another reason for the codes you have, but as a first step I would replace the DPFE sensor and check the hoses, if it is indeed the original 1995 DPFE sensor

The excessive flow could mean the EGR Valve is not closing all the way, this would cause a stumbling idle
The pinging would indicate lower flow from partially blocked EGR tube
These are not mutually exclusive, because if there was carbon build up over the years the tube gets clogged and valve can't close

 

I'll go ahead and replace the DPFE sensor. I notice there are 2 different versions of the DPFE sensor: Motorola 1.0 volt and a Kavilco 0.5 volt. Are these interchangeable or are they specific to the particular truck? The part number on my current one is F48E-9J460-BB.

 

I would say 1995 would be 1volt version for sure

 

I replaced the DPFE sensor last night and cleared the code. This morning the check engine light came back with P1401 again. Using forscan it’s showed the sensor voltage at 5 volts just like the last one did. I’m guessing either the new sensor is defective or I need to diagnose further.

 

You will need to test the voltage at the sensor
Use a sewing needle to pierce one wire at a time so they can stay connected to the DPFE

Key on engine off
Brown/white wire should have 5volts, its the Power IN from computer, this wire powers several sensors

Grey/red wire should be a Ground, its the common reference ground for several sensors, but from PCM(computer)

Brown/light green wire, this is the money wire, lol, it should be sending back .8 to 1.2volt with engine off, this wires voltage is what you see on the Forscan

If brown/green is 5volts then unplug wires from sensor and test it again, it is still 5volts then the two brown wires are shorted together in the harness or possibly in the PCM

If brown/green wires voltage drops when its unplugged then yes, new sensor may be shorted inside

 

I wanted to push this thread a bit further on the diagnosis question trail

I've got a 2000 Ranger with the 2.5L. and have only the P1401 code

I did the connector test above sticking the needles through the wire leads of the connector. Brown/White came back with 5V, Brown/Light Green came back with 1.02 so it sounded like that was good as well.

I also saw a test on someones YouTube diagnostic but not sure what it was to determin) put pins through the 1st and 3rd spot on the connector, disconnected the front vacuum line, attached a vacuum tool and pumped it up to around 15psi. The engine started to idle a bit rougher.

So, I replaced the sensor, cleared the code, drove 15 minutes, and when I turned it on again, the code was back.

Any other advice?

I'm thinking this is looking like above my skills and test equipment (ODB2 & Multimeter)

 

Are there any running issues, i.e. rough idle or misfires?

Any code that starts with P1xx means its a Car Maker specific code, so in this case a Ford code.

If it runs OK then most likely its not an EGR system fault, which means a sensor fault or computer fault
If you changed the sensor then you may have a computer fault, and not sure you can fix that, just replace computer

 

ug, the PCM issue is what I'm afraid of.

 

You can pull off the PCM(computer) connector, check for any water intrusion or dirty connectors, pin 65 is the DPFE signal at the PCM
The other 2 wires on the DPFE are ground(pin 91 PCM) and 5volts(pin 90 PCM)
The ground and 5v wires are shared with other sensors
The TPS(throttle position sensor) should have the same 2 color wires for ground and 5v as DPFE, so you can test if DPFE and TPS are the same, if voltage or ground are even a little different it would through off PCMs reading of DPFE signal in

You can use your VIN and check with a Ford Dealer to see if there is a software update, they usually charge $100-$150 to do the update if there is one, and it may not fix P1401 if its a circuit hardware problem inside the PCM
And sometimes they have a 15 year limit so won't have software for 2000 vehicle, but with the low cost of data storage now-a-days I find that ridiculous

 

Ron,

A few followup questions.

Do you know what I should have been watching for in the test where I "pins through the 1st and 3rd spot on the connector, disconnected the front vacuum line, attached a vacuum tool and pumped it up to around 15psi. The engine started to idle a bit rougher."

A friend told me I didn't give the sensor a long time to settle in. I installed it, cleared the code, drove it 15 minutes and turned the truck off. when I turned it back on, the code was there. Do you think there's logic to that?

Someone else I was watching said if you're doing one thing in the Ford EGR triad, you should do all three... what do you think?

 

Not sure of the questions?

If you apply vacuum to EGR valve, with engine idling, then engine should start to run rough, this is a test if EGR Valve is opening, not a test of DPFE which has no vacuum lines

DPFE measures pressure difference between its two exhaust hoses, one is closer to EGR Valve so will have a greater pressure drop than the other when EGR valve starts to open.
PCM uses this difference to calculate how much exhaust to add to the intake to prevent NOx emissions spiking in the exhaust

 

Ok, quick update.

I didn't have a bunch of time last night to finish the tests you gave me, but I did check continuity for the PCM pins to the sensor connector you mentioned and they came out fine.
I'll work on testing the EGR sensor connector vs the Throttle position sensor connector tonight.

I had a friend from work look over my shoulder and back check my testing and logic on some of the other earlier thought lines. He noticed a severed vacuum line that I don't know how I was missing. I guess too focused on the sensor and solenoid. Anyway that line seemed to go to something on the front towards the passenger side of the radiator. Once he found that one, he started taking off all the tubing the P.O. used to wrap the other vacuum lines and we found that at one point the hard plastic vacuum lines going from the EGR solenoid to the EGR valve, and from the solenoid to the Exhaust manifold had been cut, and then patched back together with some clear tubing (maybe heat shrink tubing).
We got some rubber vacuum hose and patched all three lines back together for a short term fix.

Now, the Ranger has a rough idle, and almost will die when cold. once warmed up it just oscillates back and forth between normal and low, and still gets the P1401 code.
...On the plus side I've got more air volume in my heating/cooling vents.

 

Check the EGR solenoid, it may be leaking vacuum to EGR Valve, causing it to open a bit which fouls up air/fuel mix

The EGR solenoid should stay closed, will not pass "air" in either direction, when engine is idling, EGR system is only used after engine warms up and above 1,300rpm
Test with engine off and then engine idling, solenoid should not pass air

 

Well, the long story short, I was running out of time, gave up and took it to a mechanic.
So, what they did,
first round: found the solenoid was failed in the open position. swapped that one out with a Motorcraft version... Also commented on the batter seeming under charged. So, take it for a long drive and watch the alternator/battery .
...took it for a 70 mile run of city, highway and freeway. got it home and tested the battery it seemed to be doing ok, but an hour later I went through a series of cycling the engine off and on testing voltage and it did dip maybe a bit too far when all the accessories/AC/Lights were on. ...and the P1401 came back on.

Round two: They found the voltage on the aftermarket DPFE sensor to be a bit flaky, so they replaced the sensor, plug and alternator with new Motorcraft.

Took it for another 70 mile tour, it passed WA emissions, My son came up and licensed it and drove it back to base (southern California last thursday/friday with no issues...
Yay, its done. :)

I had a Subaru back 20 years ago that the alternator was glitchy. The car would be running fine, then all of a sudden be running real rough and bucking, and a mile later be back to fine. A mechanic and I spent a couple weeks working on it here and there, trying different things and one day he decided to try the alternator out of another. That fixed it then and I'm kind of betting that was a contributing factor here.

Anyway, Thanks so much for the help and wisdom.

 

On my truck I measured 1v on the money wire and 5v on the supply but unplugged I get 5v on both? You're saying this isn't normal?