On my 95 Grand Marquis with only 75k miles the check engine light started coming on a while back and scanner showed P401 low EGR flow.
The EGR is in a nasty place on the 95 GM 4.6 so I took it to a local mechanic and showed him some YouTube videos on clearing clogged passages which typically is the issue.
They wanted to change the EGR since part is cheap and labor is the same but since there's not much that can actually "break" on the EGR I just had them clean it.
A month later the light was back with same code so I took it back and they said WE TOLD YOU SO to change the EGR.
They allow me to get my own parts so I took the atomic bomb approach and bought a new EGR and DPFE sensor (also a pain to replace since screw heads are facing the firewall with 2 inches of clearance) and had them replace both.
Neither were Ford OEM parts but I figured there was not much the maker could screw up on these.
After mechanic threw both in we got a P1401 DPFE circuit voltage high code... Great!!!
So now we put the original DPFE back in (OEM was metal, replacement was plastic) and P1401 went away but one week later P401 code was back.
I bring it back to shop AGAIN and asked specifically if they "REMOVED" the entire EGR plate and cleaned underneath when they replaced the valve.
They could not give me a straight answer so I tell them to take it all apart again CLEAN THE PASSAGES in the intake that get carboned up.
They claim they did this and it was not clogged and as of now I have driven about 80 miles with no CEL.
Based on past events, I am not confident it's permanently solved however.
I really don't want to live with this since from what I read the P401 CEL puts the ECM in rich mode to prevent possible engine damage and this is consistent with the car smelling like it's running rich and poor fuel mileage (<18 highway but should be about 21)
My only other thought is there is some vacuum leak causing EGR not to open enough once in a while triggering the code.
Anyone have other thoughts or comments on this mess? Thanks.

 

Hello, Joe -- and welcome to the Mercury Forums --
Not many '95 Grand Marquis around these days, and it's getting hard to find anyone that's familiar with the EGR system.
From your description of "the problem" and the remedies that were tried, I see two (2) issues:
The correct DPFE sensor is: Motorcraft DPFE 15 -- available at RockAuto and Amazon.
The Motorcraft DPFE 15 is a design change from the original. The original part was made with pot-metal, and would get hot and fail.
The DPFE 15 is made of a phenolic composition that doesn't get hot and fail.
HOWEVER, since the whole EGR system has been taken apart and cleaned, we'll ASSUME that the new parts are OK.
The issue that wasn't mentioned is the EGR Control Valve (solenoid) -- which tells the EGR valve when to open and close.
There is no adjustment or cleaning procedure for this part -- just replace it.
The EGR Control valve is attached to the firewall with 2 nuts -- easy to get at, and easy to change.
Also available at RockAuto and Amazon, but only as an aftermarket part -- Motorcraft part is no longer available -- I used the Standard Motor Products # VS52 -- still working fine after 45,000 miles of service.
I've found that working on the EGR system is MUCH easier when the entire windshield-wiper assembly is removed before beginning work on the EGR stuff.
Click on my Profile to see pix of some of the modifications that I've made to the 95 MERC.

 

Thanks for the tip on the solenoid, that will be my next step if CEL returns. It's been off for about a week now so fingers crossed. As for the DPFE I bought it looks identical to stock piece but plastic. This one was a lot less than the other non oem brands offered so I guess I got what I paid for in this case lol. 1A Auto refunded me and didn't even want bad part back. Hey I posted about a radio problem here also and since you sound like a veteran on the panthers let me know if you have any ideas on that one. Thanks again!

 

Glad to hear that you got the EGR thing under control, Joe -- if the CEL comes on again, even for a short while, replace that EGR Control Solenoid right away.
You can do it yourself in just a few minutes -- no special tools or skills needed -- saves money, too !!
There's no way that I could afFORD to restore and/or modify the 95 MERC if I didn't do the work myself -- using a variety of parts suppliers, but mostly Amazon and Rock Auto.

In order to give factual/helpful answers, it would help to know:
GS or LS ??
What state are you in ??
Anti-Lock brakes ??
Trailer-Tow Package ??
Dual exhaust ??
I have over 210,000 miles and 21 years of experience at owning, driving, restoring, and maintaining the '92 & '95 Panthers -- Mebbe I can help . ;>)

 

I'm in NJ and my car is an LS with leather seats, digital cluster and has ABS. I believe it has the HPP pkg since it has the mesh wheels, sway bars and dual exhaust. Amazingly it does NOT have the auto dimming rear view mirror which is a major PIA driving at night on the interstate. Not to go too far off topic but two other annoying gremlins lately - 1) the abs light comes on once in a while in wet weather (just when you need abs) and 2) check air suspension light comes on intermittantly. I put in a new pump and the system works fine for weeks then appears to stop checking in with the ECM. When this happens it stops venting so is slightly jacked up. These are never at the same time and both conditions normally reset after key cycle or in a few days at most. I don't drive it daily. Maybe faulty wire to abs or ride height sensors or the sensors are bad?

 

Next project for me is to send in the EATC for rebuild. Half my lights are out and it occasionally jumps to heat when I want AC and heat is not that hot in winter. After flushing core and changing tstat I bought a kit on ebay to bypass the warm AC blend door issue by controlling coolant flow with a solenoid but have not installed it yet. After reading the install manual they claim when wired to the EATC it could decrease flow to heater core flow unless i tinker with the nut on solenoid which I don't want to be doing going into winter. I have a feeling someone tried fixing the blend door in the past but not sure if its 100% or if they got it partially working. In any case I'm not going to tear the dash apart to find out.