P1401 Voltage tests

[thoorn]

I am new to this forum and to my 2002 Ranger FX4. When I bought it, it had DTC P1401 set. The original owner said that change the DPFE won't fix it and he just lived with the MIL on. I don't like to do that so I am trying to figure out why it is set.

When I test the voltages on the harness to the DPFE, I get 5V on both the DPFEGR Signal pin (pin 3) and on the VREF pin (pin 1). I don't think this is correct as it is setting the voltage over the threshold. Can anyone confirm for me that 5V should not be on the DGFEGR Signal pin? Has anyone seen this before and if so, what was the cause? I am thinking it is the PCM.

I even replaced the wire from pin 3 to the PCM to rule out some sort of short between the two pins, but I am still getting 5V on both pins.

Thanks in advance for any feedback.

 

[RonD]

Use this page for testing wires and voltage.
http://rockledge.home.comcast.net/~rockledge/RangerPictureGallery/DPFE-Voltage-Test.html

The PCM could be at fault but you need to test voltages with wires connected to DPFE because PCM uses a "reference" voltage system on many sensors, this is because vehicle voltage can vary from 12.0 volts to 15.0volts during operation.
Yes it does use voltage regulators like for the 5.0v, but those are still subject to variations based on vehicle power, so it might send out 5v on each line and then the sensor lowers voltage on one line and that is what the PCM wants to see, so if voltage was 4.5v on both it wouldn't matter, or 5.5v, it is the difference it looks for, so a "reference voltage system"

 

[thoorn]

I just wonder why there is voltage on the signal line when the connector isn't attached to the sensor. I would expect it to only get voltage from the sensor, not from the PCM. So the question would be is the PCM bad, or is something else causing the PCM to put voltage on it?

 

[RonD]

There is usually 3 wires on a DPFE sensor, all can have voltage when unplugged from sensor, only way to test is with wires plugged in.

 

[thoorn]

I get 5V on both pins 1 and 3 when it is plugged into the sensor as well. Pin 2 is to ground.

 

[Earl43P]

First thing I'd suspect is the hoses to the DPFE are reversed.
One is Ref, the other is Signal.

http://www.route66hotrodhigh.com/EGR.html < gives you an option to delete EGR and fake out the PCM (no CEL, no code).

http://www.tomco-inc.com/techinfo.aspx < more EGR Testing info.


I always liked the tech. that Joe Rockledge put out.

Another possibility is that the EGR ports on the intake are clogged with carbon.

 

[BWDuty]

P1401 My Fix

I wanted to add my experience, since this code has been hounding me for quite some time. I tried all of the usual fixes first of course.. Replaced the DPFE with one from a junkyard. That didn't work, code came back as soon as I cleared it. Broke down (figuratively, this never actually rendered my truck inoperable. Even when I had the DPFE sensor completely unplugged) and bought a new DPFE sensor, and those things aren't cheap for a 2000 2.5L. I think it set me back over $70. That still didn't fix it. After doing quite a bit more research, I found that the EGR system could get clogged with carbon build-up which has been known to trigger this code. Just to be completely safe, I replaced the EGR valve itself, the EGR tube, and cleaned the ports they connect to really well with carb cleaner. Reset the code, and bam right back on.

I had already visually inspected all of the wires, but since the code itself makes me thing electrical I decided to go a bit further. I very gently tugged on the wires coming out of the harness that plugs into the DPFE sensor. One came out with absolutely no effort, and another came out fairly easily. I suppose this could explain why replacing the DPFE sensor "fixes" the problem temporarily for some people. Handling the harness when unplugging and plugging it in might give the wire just enough contact for a little while.

The parts store wanted over $30 for a new harness, so I went around at a junk yard until I found one in which I could tug all three wires fairly aggressively and they were in there really well. Unplugged the harness, cut off enough wire to splice it to my old wires, and the problem has been fixed ever since for $2. Well, at least I have a whole new EGR system now! I guess that can't be bad for mileage.