DPFE voltage too low


New Member
Nov 29, 2011
I'm troubleshooting the following codes on my 2000 Mustang V6:

P0401-EGR flow insufficient
P0301-Cyl #1 misfire
P0174-System too lean

My voltage measurement from the signal wire on the DPFE is significantly low compared to what I've gathered from multiple sources at only 0.21-0.28V at idle. I've verified my EGR valve is operational by supplying vaccuum to it which made it run rough as expected. I have also made sure all passageways are clear. One post I read said to monitor the dpfe signal voltage as I applied vaccuum to the ports on the sensor itself and showed no change in signal voltage. This leads me to believe my dpfe is in fact bad. Am I missing something?
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SN Certified Technician
Aug 14, 2009
Houston Texas
To trouble shoot this, first verify that all vacuum lines to/from the DPFE are leak free. Exhaust gas is hard on rubber parts. Don't cut corners here.

Next check to see there are no exhaust leaks as this will cause a false DTC.

Double check that the electrical connector to the DPFE is clean.

IMO, about half the time the DPFE sensor is at fault. Remember that exhaust gas is hard on these parts. This is followed by blocked TB passageways and then a bad EGR value.

Further, Ford has changed the calibration to reduce the number of false DTC codes. A new unit will have this updated calibration.

My recommendation based on what you have already done is to replace the DPFE.

What have you done to rule out a vacuum leak for the lean DTC?

Check the fuel injector on #1.
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