Dec 18, 2019
Chicago, IL
Hey all!

I've got a 2003 Convertible GT reading: P0403 OBDII: Exhaust gas Recirculation (EGR) - circuit malfunction. Does anyone have experience troubleshooting this?

I've read things from simply an o2 sensor which would be great and I've done on another vehicle before, but it sounds like it's the whole circuit. I saw another post saying the P0403 code is tied to fuse 8 in the under-dash fusebox so I pulled that, but it looks good to me. Other than these, I've seen the EGR Vacuum Solenoid being the problem, any way to confirm this before replacing it? Thanks for your help!
  • Sponsors(?)


SN Certified Technician
Aug 14, 2009
Houston Texas
Just wondering. Are you sure that the correct code has been posted? The P0403 DTC is associated with electric EGR system which the Mustang does not use.

But in general. Anytime the DTC calls out a circuit malfunction it means there is something soooooooo wrong with the circuit that the PCM is unable to perform any diagnosis. Think:
  • Bad DPFE sensor
  • Wiring fault. IE bent/pushed/dirty connector pins or damaged wiring harness.
  • Ground fault or short to power.
  • Bad PCM.
In my experience the DPFE sensor fails at a fairly high rate. If this were my car I would start with a visual inspection of the DPFE connector. If no problem found, replace the DPFE sensor.