P0401 - Replaced Entire EGR System | Ford Explorer Forums - Serious Explorations

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P0401 - Replaced Entire EGR System


New Member
June 5, 2023
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City, State
Year, Model & Trim Level
2010 Explorer XLT 4.0
Hi all new member here.

First things first. I've used the search function and have read all applicable threads before posting.

I have a 2010 XLT with a never ending emissions problem. Started with P0401, P0403, P0443, P0455 and finally P0457.

I have spent many hours researching, diagnosing and repairing myself before finally going to a "reputable" shop. My experience went about the same as every thread I have read about EGR systems and ended with over $1,200 spent and no resolution.

The following have been replaced by myself / shop:
  • EGR Valve (it has the integrated DPFE sensor)
    • Shop said the aftermarket I replaced with was "working intermittently". I begrudgingly accepted their absolute determination that this aftermarket part was faulty and after much resistance and hesitation allowed them to replace it. (spoiler alert: it didn't fix the problem).
  • Engine Vacuum Harness (lines were cracked)
  • EGR Vacuum Regulator Solenoid
  • Exhaust Manifold Tube
  • Port from EGR to intake manifold has been cleaned
  • Engine will rough idle / stall upon applying vacuum to EGR valve
  • Engine vacuum has been confirmed good

I have an engine coolant leak at the thermostat housing. So a replacement thermostat and housing are in order. (shop want's $1,100 to replace or I can put my own blood sweat equity into it)

My question is: Can a P0401 code be at all related to losing engine coolant and insufficient temperature differential?

It takes a good 20 - 40 min of driving to set all the the monitors ready for SMOG and as soon as the EGR monitor goes ready the P0401 code is thrown.

Due to CARB and BAR in the never ending nightmare that is California the P0401 appears to have also registered as a permanent code. This requires 200 miles of driving and 15 warm up / cool down cycles to ignore the permanent code.

I have found one reference to P0401 and a new thermostat here: P0401 code. I'm hesitant to raise a thread from the dead, but unless I can resolve this California says the perfectly good vehicle must be thrown away.

EDIT: upon rereading the thread the thermostat reference P0401 code was probably in regard to P0125 in OP's initial thread.

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According to Fords Service Information for P0401 for a 2010 Explorer, these are the possible causes.

P0401 A.jpg

This is the first pinpoint test for P0401 below. Is this the only code you have now? Do you have a scan tool that will allow you to do a key on engine running test?

P0401 B.jpg

I have seen the third to the last possible causes (hoses reversed) that caused a P0401 that was hard to diagnose because all parts were new.
When a situation like happens you fall back on what could have gone wrong.
If the hoses are installed backwards the voltage will go down towards 0 instead of going up towards 4.50 volts like it should.
That would cause a P0401 all day long.
Dont know if that is possible on the ESM type egr valve.

Wait, something isnt right. You said you have an integrated DPFE sensor.
If you do then it also has an integrated EGR solenoid.(but it is listed separately on your list of parts) Can you take a picture of the egr valve and post it here to eliminate any confusion.
I will try to help as best as I can.

Hey just wondering if you ever solved this. I am going through a similar headache; very similar diagnostic "path" with P0401 and P0457.