I know a bunch of this stuff get's hashed over and over guys, but I did read through a number of post and still would like to know what the most common solution is to this code. I checked the voltage to the EGR and the DPFE and the voltage is within spec. The resistance on the EGR is within spec. I did just run seafoam through the truck about a week ago and replaced a bad O2 sensor. No new codes until now. The book calls for a test of the DPFE involving a backprobe while the engine is running cold, then warm, but I am not sure what the heck they are talking about with the backprobe stuff. I barely know how to operate my voltmeter? Does anyone pay any attention to this test, or is replacing (I have read about making sure the vacuum lines are not clogged) the DPFE sensor just the routine procedure?

 

Have you tested the EGR valve and the intake ports yet? Simple test.

See my post a couple of days ago in the thread about the P1401 code. If that test passes, the the DPFE is most likely the problem.

Steve

 

Check this out. I had the smae problem.

https://www.f150online.com/forums/sh...ighlight=po401

hope that helps.

 

I tested the signal voltage and the reference voltage on the DPFE sensor and the signal voltage. The one voltage is supposed to read up to .70 volts cold with motor running, and eventually go up to 4-6 volts after warm up. Mine DPFE never rises above .92 on this test, regardless of how long I let the truck warm up, so I am under the assumption that the DPFE is bad.

 

DPFE voltage changes with egr flow. engine temp.has no effect on DPFE voltage. To test DPFE sensor monitor voltage like you did and apply vaccum to the reference port on the DPFE sensor , voltage should increase as you increase vaccum . The 2 ports on the DPFE sensor are marked,look for REF. .92 volts with no vaccum is good. voltage should increase to around 4 volts . BE SURE YOU ALSO CHECK EGR PORTS FOR BLOCKAGE AS DESCRIBED BY OTHERS!!!!!Let us know results.

 

Stan,

Not to dispute you but why does the book (Haynes Manual) say that the DPFE test should involve backprobing the terminal for signal voltage while the engine is running, first at cold (No EGR) and the voltage should be .2 to .7, and as the engine starts to warm (EGR is signaled) voltages should increase to 4.0 to 6.0 volts?

I don't have a tool to apply vacuum, as you mentioned, and I should mention that I get no stalling when I place my finger over the vacuum line going to the EGR, or over the EGR nipple itself. The crazy thing is I got the additional code P1401 tonight as I drove up the road about 25 miles, and then the MIL light did not even come back on when I started back home tonight, and the codes did not return after having erased them on the way home. I ordered a DPFE sensor from Advance Auto, but I will have to do some more testing in the morning.

 

karkfump I am a ford sr. master tech. The test I suggested is right out of the ford manual. The PCM(computer)checks egr flow by pressure changes at the DPFE sensor. DPFEstands for DIFFERENTIAL PRESSURE FEEDBACK E=EGR SYSTEM. YOU NEED TO APPLY VACCUM TO THE EGR VALVE TO CHECK FOR BLOCKED PORTS. If you don't have a vaccum pump,hook a piece of vaccum hose to any vaccum sorce on the engine. With engine running apply vaccum to egr valve. Engine will stumble or die if ports are clear. I can't think of any reason your manual has you testing voltage hot and cold, when it is pressure that changes voltage. That would make it DTFE( DIFFERENTIAL TEMPERATURE FEEDBACK)

 

Everyone has the needed vacuum source. Just pretend it's a milkshake. You can call it your "Personal Facial Vacuum Source".

The Haynes is flat-out wrong about the temperature of the engine. EGR is never called for by the computer when the engine is cold (or at WOT).

You can backprobe that signal wire while activating the EGR valve. If there is EGR flow (ports not blocked) AND the sensor is good, you will see a DC voltage proportionate with the amount of EGR flow.

Steve

 

I don't think the Haynes manual is suggesting that the temperature is effecting the voltage, rather the EGR is simply closed as both of you guys have mentioned when the engine is cold, and as the engine warms the EGR does eventually open up, thus efecting the voltage. I will try the milkshake vacuum test on it now, and post the results, before I go pick up the DPFE sensor.

 

Did the vacuum test on the EGR, and the motor stalls just like it should, actually killed the motor once. So I assume this indicates that the ports are not clogged and the EGR is ok.

 

Replaced the DPFE sensor after getting the positive results on the EGR test, and so far I have not experienced the return of any codes. Drove around 125 miles today witht he Actron scanner plugged in, and all is well, at least for now. Thanks guys for the vital information.

 

The PCM does not allow the EVR solenoid to supply vacuum to the EGR valve until coolant temp is somewhere over 100F. That does not prevent testing the DPFE only with the engine off. Pull the two differential pressure tubes froim the DPFE and check tubes for blockages. If clear, check the DPFE ports for corrosion and moisture. Hook vacuum to ref port (small port on front) using a hose and sucking on it if no vac pump is available. Backprobe means to probe the back of the connector with the unit hooked up normally. You'll probably need to pierce insulation with a pin, but best to use probes with very sharp and thin points. Voltmeter + goes to top wire and voltmeter neg goes to middle wire. Turn key on, but do not start. Voltage should climb smoothly to over 4V as vacuum is applied, and smoothly drop to near zero as vacuum is released. This means that THIS PART is working. Remove green vacuum hose from EGR valve and hook up your vacuum tube. Start engine and idle. Engine should stumble or die if EGR valve works and passageways are clear. Otherwise, you need to clear the throttle body EGR ports, EGR valve (visually check for smooth operation with vacuum and there should be no vacuum leak in actuating diaphragm), and EGR tube differential pressure restriction passageways. These are quick and easy tests and should spot over 95% of problems. You can hook your vacuum test tube to the green hose from the EVR solenoid and check for vacuum while running and blipping the throttle (engine must be warmed for this test, because exhaust gas recirculation is NOT used in an F150's cold engine, regardless of what anybody else tells you, unless my Hayne's manual is lieing. This is a PCM/EVR/DFPE system test, NOT a DFPE only test. The EGR valve and passages are tested by actuating the EGR valve at idle.). If vacuum in the green hose changes, the PCM is telling the EVR to apply vacuum to the EGR valve for some exhaust gas in the intake plenum. You can lock the EGR valve open with your vacuum tool, and see that exhaust gas is never called for by the PCM because it will already be flowing at the max and the DFPE should be telling it so. The DFPE sensor is the gizmo that measures the differential pressure in the exhaust tube across the restriction between the two sensor hoses as the gas flows through it. If the sensor is hanging or in the wrong position, the wrong amount of exhaust gas is allowed into the intake plenum because the PCM is being lied to by the DPFE sensor and you got problems, dude. That means maybe a P0401 code, or something else if it is too high flow, or a hard failure. Like your O2 sensors may be fooled by the excess exhaust gas and lean out the fuel/air misture too much. Ping, ping, ping.

This may not be the XYZ, but it is the 123 and ABC of DFPE, EVR, and EGR valve testing and it may be all you ever need. It nailed my problem down and solved it.

To make this really simple, it only takes two Pollacks to test this system. One to suck and release vacuum on the EGR valve while the other Pollack monitors vacuum in the green vacuum hose and fiddles with the throttle. I'm French, so I can do this by myself because I can suck, fiddle, and feel at the same time.