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Q: P401 Code on 2000 Ford Expedition

I have a Ford expedition 4.6 and continue to get a P401 code. I have replaced the EGR manifold, sensor and DPFE sensor. I also had an intake cleaner with ISC with the machine done and still continue to get the same code. What else could be the cause of the P401 code? I have changed all the EGR parts and put pressured air through all the tubes (manifold, sensor & DPFE numerous times with no avail) The trucks starts but I can’t seems to find the answer to this darn code.
Thank you in advance,

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If all the passages are clean, it could be the EGR Electronic Vacuum Regulator Solenoid # F63Z9J459AA,
Purge Solenoid# F75Z9C915AA
Also a bad ECM, wiring problem or vacuum hoses.
These could be all diagnosed by a diagnostic tech. It worth to pay the diag. fee so you don't need to replace unnecessary parts.


One more thing, remove the throttle body and check the ports there too. They might be clogged.
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