Hello all. I have a recurring P1401 code. New dpfe, Working EGR. EVR solenoid seems fine. Have good power and vacuum to parts. When applying VPWR battery ground to ground return side of EVR solenoid thru a small test lamp, the Evr solenoid opens the egr valve and engine approaches stall. DPFE appears to respond as well with correct voltage increase. It runs about 1 volt to around 4 under demand. 1996 Mazda b2300. Last 8 of VIN is TTMO4289. What is the correct dpfe? Is it a .55 volt model, or 1.0 volt? I probably have original PCM and it probably has never been reflashed. I installed a cheap 1 volt aftermarket BWD dpfe from Advance. Does it matter which voltage dpfe is used? Will it mess up the computer? I need to know if I have a bad pcm, or possibly an open or short between the EVR and PCM. I may be lacking return ground between the pcm and my EVR. I have a good coil and power at the vacuum solenoid. I do not have scanning tools. only a meter. It may not be pulling vacuum when needed. Not sure. What is the PCM EVR ground return pin number, and correct test procedure? Does the newer 1 volt plastic replacement dpfe cause an original non updated pcm to sense a failure? Will it send a fault code? Will it allow EVR system to function fully, partially, or not at all? Will it function and just throw off a CEL? When I clear codes and relearn PCM. Truck seems to run well and no CEL comes on. But, after I shut it off and then restart it, the CEL throws the code again. What gives? Do I need to just drive it, or is there something wrong, like a bad PCM? I just took one more drive and relearn and then shut it down . I will wait 8 hours before restarting it and look again. I looked over a lot of info. I could not find the answers that I need specific to these early model OBDii pcm trucks. Please help and explain so that all of us can benefit. Thank all of you.

 

Welcome to the forum

EVR solenoid will usually get 12volts with key on, the Ground wire runs to PCM(computer), similar to how IAC Valve works.
Computer Pulses the Ground to open EVR solenoid a little or alot as needed.

DPFE sensor has two hoses connected to exhaust system
One hose is closer to the EGR Valve than the other
As PCM grounds EVR solenoid the EGR Valve starts to open, when that starts to happen the closer hose has a Pressure drop.
How much the pressure changes compared to the other hose tells PCM how far open/how much Exhaust gas, is flowing into the intake.
DPFE = Delta/Differential pressure feedback sensor

P1401 means DPFE sensor wires may be damaged or the sensor is.
Long shot is PCMs internal circuit for DPFE is bad.

Make sure the two DPFE hoses are clear, they get water build up inside, and no cracks, these are exhaust hoses not vacuum hoses.

But code is more about the circuit wiring than the mechanical aspect of the EGR system

This PDF explains voltages for Ford DPFE sensor wiring: http://www.tomco-inc.com/Tech_Tips/ttt35.pdf

The Computer/PCM supplies a few sensors with 5volts, MAF, TPS and DPFE are some of these.
The Return voltage is what the PCM uses as Feedback.
So if DPFE is getting 5volts and sending back .45v then there is 0 pressure difference.
If PCM is getting less than .45v then "it is out of range"
If more than 4.5volts then "it is out of range"

DPFE signal is 5volts
VREF is a ground
Signal return is the .45 to 4.5volts


PCM won't set codes on 1 failed test of the EGR or EVAP system
Usually there needs to be 2 or 3 failed tests in 2 or 3 drive cycles, for an emissions code to be set
Drive cycle is one heat up and cool down of the engine, not key on key off

And it can take 2 or 3 PASSED tests for the code to clear.
I think a Ford Dealers OBDII computer can clear emissions codes but not retail units

 

Thank you RonD. I have DPFE voltages. I get between 1 volt and about 4 volts under load.. I think it is good. When I force the egr system to function by supplying ground to the EVR, the system works and pulls vacuum to the egr which works well. It stalls the motor. I am wanting to know if I may have a problem with having the correct voltage DPFE. My PCM is probably the original, and the old DPFE looks to be the original metal one. The old one may be the .55 volt model. The newer replacements are a 1 volt model. So, I am needing to know if there is a problem with the computer picking up the at rest voltage of 1 volt on the new replacement DPFE instead of the old DPFE's .55 volts. Do I need to reflash my computer in order to clear the code P1401? Or, will the PCM eventually allow itself to accept the new DPFE voltage? If I lost signal ground from the EVR to the PCM, I would expect to get an under volt code and not an over volt code. Is the PCM giving me a false flag CEL? Thank you.

 

Not sure they ever used the .55v models on Rangers/Mazda but maybe they did.
The metals ones were .55 or 1v, plastic are only 1v

If you referenced 1996 Mazda B2300 then you would probably get the plastic one if it was 1v model as that would be current replacement.

Not sure what to tell you out side of going to Mazda dealer and have them source the part just to see what part number they come up with