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Troubleshooting EGR Error Code P0401


Behmer99

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Hello fellow forum members -

Long time lurker that's picked up lots of useful information, but am now in need of some help.

I'm working on my 1996 Ranger with a 4.0L. It has the P0401 EGR Flow Trouble Code.

I've read countless postings on here to try and learn as much as I could. From what I could tell, I thought it was the DPFE sensor, so I picked one up and replaced it. No luck -> still get the error code.

I've started over and am walking through the steps listed here: http://easyautodiagnostics.com/ford_egr_test/ford_egr_valve_1.php

Test 1 for testing the EGR Valve seems to pass. If I apply vacuum to the Valve nipple, the truck idle's rough and the vacuum does hold (so I don't think it's a diaphram issue). Releasing vacuum and the truck idle's normally.

Test 2 - This one get's me and I've performed it on both the first DPFE and the new replacement. This is testing the DPFE EGR Flow signal. With KOEO, I get a reading of about .6 volts on the old DPFE and about .4 -.5 volts on the new DPFE. If I apply vacuum to the valve, instead of the voltage rising, the voltage drops to around .2 volts. I'm not sure what this means. I haven't gone onto test other things at this point as I'm not sure what this could mean. I've also tested the circuit itself and it's reading right around 5 volts, so I believe the wiring to be OK.

Hoping someone with some background in troubleshooting this could help me out. None of the vacuum lines appear to be damaged and all seem to be connected.

Thanks!
 
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Rock Auto 5% Discount Code: F9A1A579ACFAD1: October 1st, 2021

Earl43P

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Behmer99

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Well Earl43P, I owe you a huge thanks! All the issue was is that someone had switched the REF and HI signal hoses going to the DPFE. This thing has only been serviced at a Ford Dealer, so that possibility had never even crossed my mind that the tubes would be switched up. Lesson learned to never overlook even the simplest fixes.

Thanks again!
I like Tomco's EGR site better for troubleshooting and info (http://www.tomco-inc.com/techinfo.aspx).

If you are sure that you have the DPFE Reference and Signal tubes connected to the proper nipples on the DPFE, then I'd guess you have blocked ports.

http://www.tomco-inc.com/Tech_Tips/ttt35.pdf
 

brandothehick

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Hey i got a 96 to and i get p0401 as well. i changed out my whole egr system and a month later i still got the code, so i went to to have it looked at and the mechanic said that it just happens with the mid 90s rangers and its just the sensor is off not the egr system. He told me not to worry about it, the light might come on every few weeks but just get it cleared nothing is really wrong.
 

Behmer99

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Hey -

I haven't spent as much time on this forum as others, but my understanding of this error code is that it should be something you can resolve. When you say you've changed out your entire EGR system, does that include the DPFE Sensor? That seems to be the common problem with these vehicles.

Other than possibly poorer gas mileage, I'm not sure if there is other damage that not fixing this issue can result in.

Hey i got a 96 to and i get p0401 as well. i changed out my whole egr system and a month later i still got the code, so i went to to have it looked at and the mechanic said that it just happens with the mid 90s rangers and its just the sensor is off not the egr system. He told me not to worry about it, the light might come on every few weeks but just get it cleared nothing is really wrong.
 


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