Got a 1999 Ford Ranger 3.0 Flex Fuel. Chk Engine light came on & P401 found.

After reading volumes of P401 Error posts, I checked the voltage output of the original DPFE... Per postings, KOEO Voltage should be .8 to 1 Volt.. Mine was 1.25, so I purchased a new one.

1 Day after installing and clearing codes, "BAM", the CEL was back.. Same code. AND VOLTAGE WAS 1.26 for the NEW DPFE !!!!!

I'm at a loss... Input voltage is 5.0, as is supposed to be.

HELP!!!!!!!!!!!!!!!!!!

 

P0401 Insufficient EGR Flow Detected
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• DPFE sensor signal circuit is shorted to ground
• DPFE sensor reference (5v) circuit is open or shorted to ground
• DPFE sensor downstream hose off or plugged
• DPFE sensor hoses both off, loose or damaged
• DPFE sensor hoses connected wrong (reversed)
• EGR orifice tube is damaged or restricted
• PCM has failed

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Lots of possibilities for insufficient EGR flow.

Seeing as how the EGR feedback flow is low & the EGR valve is controlled by the computer through a vacuum switching valve that Ford calls a EVR, (Electronic Vacuum Regulator), that part of the system also belongs on your suspect list.

So, maybe also have a look at & test the EVR's diaphragm & it's vacuum line to the EGR valve & the EGR valves diaphragm for vacuum leaks.
If you don't have a vacuum tester, most autoparts stores have a "Mighty Vac" tester in their "Loan-A-tool" program, for a refundable deposit.

If the EVR diaphragm. or vacuum line between the two is dryrotted, cracked, split or doesn't fit tight at it's connection points & leaks controlling vacuum, the EGR valve will get a weak operating vacuum signal & misbehave.

Same if the EVR's internal switching valve sticks & doesn't open enough to apply full operating vacuum to the EGR valve.

If the EGR valves diaphragm is leaking vacuum, it'll not open properly & give insufficient EGR feedback flow.

If the controlling electrical signal the computer sends to the EVR is corrupt, that'll cause the EVR to act out & miscontrol the EGR valve.

And of course if the DPFE sensors output to the computer is corrupt, that'll cause the computer to miscontrol the EGR valve through the EVR.

So, make sure the EGR system vacuum lines are leak tight & the VSV & EGR diaphragms are able to hold a vacuum, then retest the electricals for the DPFE & EVR to make sure they're within range..

If you've been using the wrong service grade, or a low grade of oil, or wrong octane gas, or the engine consumes oil, or you have, or have had other engine managment problems & ignored them for a while, carbon in the EGR feedback orifice tube assy, carries a higher probability.

So check the EGR valves feedback orifice tube assy, to make sure none are clogged with carbon as that can affect the DPFE's PID feedback to the computer.

Along with inputs from the DPFE sensor, problems with the ECT sensor, TPS, MAF sensor, TCC system can also affect the EGR systems operation, it's all a vicious circle!!!!

SO, do you have any other trouble codes???? If so, post all of the code Numbers.

If all that checks out, it's possible "Murpheys Law" is messing with you & the new DPFE sensor is bad.

A whole bunch more thoughts for consideration.
Let us know what you find.

 

Well.. I'll have to pull the codes again. As for the EVR, that was replaced as well...

Was I incorrect in using the voltage check and results as a guide for replacment of the DPFE? Is the 1.25V reading acceptable and I therefore wasted the money purchasing a new one (and getting the same voltage reading)? Can someone validate that checking the voltage actually means something??

The mystical search continues.

 

Well, for instance if the EGR valves orifice tube assy is carboned up, it could cause the DPFE to put out a corrupt PID to the computer.

If any of the vacuum hoses to the DPFE sensor are compromised, leaking vacuum, or clogged up, that could mess with the PID it sends to the computer.

So there are a number of other things that can cause the DPFE sensor to output what ever signal it sends to the computer, so we have to take All of that into consideration when doing a trouble shoot.

The EGR system is a mature & rather rugged system, so In most cases, look for something simple, like a bad rubber vacuum line or loose fitting, or carbon build up in the EGR orifice tube assy, or maybe a leaky EGR or EVR diaphragm or vacuum line.

Seeing as how the EVR has been replaced I suppose it's kinda low on your suspect list, but with Murpheys Law being what it is, I wouldn't take it off the list yet!!!!

Get a vacuum tester & check the EGR & EVR diaphragms to make sure they're holding vacuum & that the interconnecting vacuum line is holding vacuum.

The DPFE voltage you posted was measured under what operating conditions?????

 

Voltage was checked with "KEY ON, ENGINE OFF" as the process I found specified.

The 1.25V I got didn't match any of the 2 voltage ranges listied, as both were 1volt or less (3.0L or 4.0L). Mine is a 3.0L Flex Fuel (1999).. Is 1.25V acceptable for this engine??



I'll try to get the codes read sometime today and post any additional ones.

 

I'm still not clear on how, where, or what DPFE voltage your measuing.

Is it the Sig Return, or V-Ref voltage that your measuring & are you doing it by back probing with the DPFE connected????

Disconnect the DPFE electrical connector, check V-Ref at KOEO, it should be between 4.0-6.0 volts, IF the battery voltage isn't low & the PCM isn't acting out.

The PID the DPFE sends to the computer will vary, depending on the engine temp & what we're asking the engine to do. So a change in exhaust pressure & intake vacuum, will change the DPFE's PID to the computer.

Your problem isn't that the EGR valve doesn't work at all, just that EGR flow is low, so the system is working, just not providing enough EGR flow for some reason.

BTW, the new EVR regulators coil resistance should be between 30 & 70 ohms.

So, do you have any spark knock/engine ping while driving????

 

AH... Doc I had said with DPFE electrical connector CONNECTED, check DPFE Signal with KOEO, it should be approx .45V plus or minus .25V for 3.0L.. My original DPFE was Aluminum, the new one is plastic... Both read in the 1.25V range.

So I hope you understand why I'm totally Confused..

 

I understand your confusion & you can help us help you unravel your mystery P0401 code if you'll measure & post the systems V-Ref voltage as I outlined above, when you post any additional trouble codes you may have.

If the V-Ref voltage to the DPFE sensor is out of tolerance, the DPFE sensor will likely put out an out of tolerance PID signal reurn value to the computer, so right now we don't know why your getting the DPFE signal return reading/s you've posted.

Could be that both the old & new DPFE sensors are bad, or maybe their both ok, but are being fed an out of toleance V-Ref voltage!!!!

Is the DPFE test document you refer too, the one in this forums "Tech Info" thread????

The root cause problem would be much easier to find if you had an outright failure of something, but as it is, the system is working, but not quiet like it should & a number of things could be invoved.

So make sure the basics are fuctional, like the V-Ref voltage to the DPFE sensor, the vacuum control system is leak tight, then move to more detailed system tests like resistance measurements of the EVR solenoid coil & voltage checks on what the computer is sending to the EVR & inspection of the EGR valves orifice tube assy deposits & if any of those orifices are clogged with carbon deposits.

Keep us posted on your findings.

 

Sorry for the big lapse in time since I started this thread..

Well.... As requested, I checked the V-REF voltage with KOEO and DPFE disconnected.. 4.99V

Also, have replaced the vacuum lines connected the EGR and Exhaust Tube, EGR, and the tube from exhaust to EGR.

Cleared the error, drove it home, and the next day while driving back into town... you guessed... CEL popped back on..

Where to next???

 

OK, good feedback on the DPFE Ref voltage, it's right where it should be, between 4-6 volts.

Now check the EGR systems EVR/vacuum switching valve coil resistance. It should be between 30 - 70 ohms & post what you get.

If the EVR checks ok, then disconnect it's vacuum line that runs over to the EGR valve & apply 5-6 inches of vacuum to it & see if it'll hold vacuum, it should if the vacuum line is good & the EGR diaphragm is ok. The EGR valve should move open too.

If that checks out ok, connect a piece of vacuum tubing to the EVR, where you have the EGR vacuum line disconnected & try to blow back through it. You shouldn't be able to if it's workng right.

If thats ok, disconnect the EVR's electrical connector, ground one pin & apply B+ to the other one & see if you can blow through it. You should be able to if it's working properly.

If thats ok, turn the ignition to KOEO & check the EVR's electrical connector for B+ & post the voltage you get.

If thats ok, you'll need a scope & breakout pigtail to measure the duty cycle of the pulse width of the voltage signal the computer is sending to the EVR, to see if it's pulse width is changing/getting wider, as it should when the system is calling for more EGR.

If thats ok, & you know the EGR orifice is clear of carbon, suspect the new DPFE sensor has a probem.

A whole buch more thoughts for consideration. Let us know how your trouble shoot goes.

 

If you put in an aftermarket DPFE, you need not search any further. It is very common for the light to come back on when a cheap aftermarket unit is used.

 

Oh, I forgot to post that the EVR has also been replaced..

In response to KhanTyranitar... I've put both a new DPFE and a DPFE off of a fully functional vehicle having no problems..... same results.

I've also swapped out the vacuum lines to the EVR... (I have a complete 3.0L from a 98 Ranger that had no problems, but the owner wanted an engine from an ARCA car and 5 speed installed).. I've got the DPFE from this motor, (and a perfect 48K mile 1996 Taurus I inherited that runs like a clock.. I can take the DPFE off it as well), if necessary...my thought process was "if it didn't shoot codes, the part should be functional..

I'll see what I can find while following the troubleshooting process that pawpaw posted..

PawPaw....Any other places or things to check, if my logic that the parts swapping I've done is solid, and the vacuum tests show nothing????

 

Do the above tests, post the results & lets see what they suggest you should do next.

 

try DPFE2 not DPFE15. The older 1991-1999 require .5v ref. Most of the newer DPFE's (DPFE15) that say they replace the older ones are actually out of tolerance or very close at "key on". If their output is over 1 volt at "key on" they will more than likely cause a CEL in a 1991-1999 ford egr system