2003 Ford Expedition 5.4L / DPFE Sensor Wiring/ Repeated Failures

Don Keyhotay · Dec 10, 2020

I bought a used 2003 Ford Expedition 5.4L 4x4 and have put maybe 500 miles on it.

Shortly after buying it, I noticed a decline in fuel efficiency (9-10 mpg/city) and some hesitation/stuttering at 1200-1500 rpm (35-40mph). It threw a P0401 code. The DPFE (Differential Pressure Feedback Exhaust Sensor) was cracked, as was the larger hose leading to it. I replaced the DPFE and both hoses. The car ran great for about 40 miles, fuel efficiency immediately shot up to 12-13 in the city and the engine ran smoothly. Then the P0401 came back. Fuel efficiency immediately went back down and the hesitation came back.

As the DPFE was new, I figured that it couldn't possibly be the cause, once again, of this code. After investigating many possible other causes for this new code, I circled back to the DPFE and just decided to replace it to see what would happen. I replaced the DPFE again and, like magic, the car ran perfectly again...for about 40 miles and now we are back to square one.

So, I ran through the series of EGR and electrical diagnostic tests, as seen on this website: Part 1 -How to Test the Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor - https://easyautodiagnostics.com/ford/4.6L-5.4L/how-to-test-the-egr-system-1

My car passed all these tests, but I have doubts about the results of Test #8.

My question is in regard to the DPFE sensor ground return (wire #2 in the attached image).

I back probed that wire (sensor ground return) and before the key was even turned to the “on” position” that wire was showing 11.8 volts. As soon as the key was turn to “on,” the voltage went up slightly to 12.23.

So, my question is this: is that ground wire supposed to be energized with 12v even before the key is turned to “on”? If not, what kind of problem am I dealing with?

Thanks for any help you can offer!

Dan · Dec 10, 2020

What country are you in?

Don Keyhotay · Dec 10, 2020

Dan said:
What country are you in?

USA

PEG · Dec 10, 2020

Hi,without seeing any wiring diagrams,or knowing any other faults,it is a bit guessy.....but a ground wire should be 0V in reference to a ground or negative. There are several reasons why a wire you are certain is a ground,gives the voltages you list,and a faulty differential sensor,is not one.

If any diagram or test information,gives you those three wires,as Ground,Signal and 12V/5V....then the ground should be 0V.

I would double check your testing/tester,as i would not expect a supply voltage at that component,soon after ignition off. It reads a pressure differential between gas pressure,inlet side and outlet side,which is an engine running signal.

Don Keyhotay · Dec 11, 2020

Thanks very much for your reply and I will try to hunt down a wiring diagram. I should have mentioned that because of the repeated DPFE performance irregularities, I now believe there is some underlying problem that is causing the DPFE to not work properly (as opposed to the DPFE itself being the cause).

I have just discovered another related problem, which might be a more precise indicator of a wiring problem or Powertrain Control Module problem. In that same attached photo, the uppermost wire is the signal wire, the middle is the ground, and the bottom is the reference.

I just ran a test on the signal wire. According to the Haynes manual, with the engine running cold, that wire should show .2 to .7 volts. When the engine reaches normal operating temperature, that voltage should move into the 4-6 range. When I ran the test, my signal wire was about .8 with the engine running cold and never got beyond 1 volt, when at operating temperature.

Is it correct to say that this is likely a bad wire or a malfunctioning Powertrain Control Module?

By the way, I am a total novice when it comes to these issues, so thanks for your patience!

PEG · Dec 11, 2020

Hi,if the reference voltage to that sensor is 5V,you should not see 6V,as per Haynes,so not sure if all your data is correct.
Just going off standardish,older school type sensors,the higher voltages,up to the reference,5V,would indicate obstruction to the gas flow.

All these systems are prone to lots of variety,not including faults and alterations....if you are seeing no change in signal voltage,and you are certain the output IS a voltage,and not PWM or anything else....then it is possible the DPF has been removed {physically),and therefore the two pressure sensing pipes,see the same system pressure = no differential.

There are all sorts of deletes out there....some are proving "troublesome" this side of the ocean,with a simple £300 delete done,a couple of years back,now raising the spectre of very costly repairs,to put back,to MOT standard......some commercial vehicles £10,000+ a piece?

I would ensure,that before you continue with the standard set of tests,you confirm,the vehicle is "standard".

Any previous alterations.or issues,can cause erroneous test results,and going off on a tangent.

Just had a quick look at those test procedures,in that link....did not work,last night...their method of testing ground,is not what i would rely on,especially with just any multimeter.

I proves "some" ground,but not "a" ground. A reading of 12V between this and the battery positive terminal,merely shows a link. I would be happier to get a continuity reading,in Ohms,between this wire and true ground,or negative.

You can demo this to yourself,by reading battery voltage on your multimeter,between battery terminals,then placing something between one probe,and a terminal,like,a wet hair,cloth,,,or tangerine.?

The readings will be interesting,but no use.

Don Keyhotay · Dec 12, 2020

Thanks very, very much for taking the time to provide such a thorough answer. I decided to turn my attention to testing the fuel system and quickly found a failed fuel pressure regulator that was causing similar drivability issues as the failed DPFE. Thanks again.