Here is what the system looks like


Usually the culprit is the DPFE sensor - that's the black box where the 2 hoses connect to. The metal tube attaches to the EGR valve on one end and to the exhaust manifold on the other end.

For a car with lots of miles, it's not a bad idea to replace the EGR itself as well, but can be a pain to access.

Other things that can throw the code with good EGR, DPFE and if vacuum lines are ok:
- the EGR tube may have a crack or be broken. That corrugated part of the tube is designed to allow some flex but can get stress cracked over time.
- the tube is designed with a little internal orifice (restriction) to allow one of the gray hoses to have higher pressure than the other under load. The DPFE sensor reads the differential in pressure and then controls the opening/rate of the EGR valve. If one of the hoses is cracked, it will throw that code. Do not replace with gas line hose, it won't last, get the proper replacement silicon hoses.
- I have found it's easier to just remove the upper plenum and intake elbow to access this stuff. Plus that allows you to be sure that the EGR passages on the inside of the intake are not carboned up (another cause of the code). Use new gaskets when re-assembling, they are cheap insurance. Caution - put a rag in the intake so you don't drop anything into it and remember to remove the rag!

Well, I've been living with the infamous P0401 code being tossed over the past month. $165 to replace the DPFE (no time or garage to work in) and $390 to replace the EGD and the tube to exhaust. 100 miles later the code is back. Not sure what else to do.

Any ideas?

Kyleaz and travelmedic,

By just replacing the entire EGR system, you are probably wasting money. Try simple stuff first. Pull the throttle body and clean the EGR ports. This is the likely main cause, and doesn't need a garage as long as the weather is OK. As for time, probably could be done in an hour. It would take me 2 hours, and I'm the slowest guy on this forum when doing stuff.

If you want to change anything just for the sake of doing so, I'd only change the DPFE.

Unfortunately my "technician" has recommended the above. I'm in the busy season and don't have the time to mess with it, so I guess I'll just burn some more $20 bills...

How does one pull the throttle body and clean the EGR ports?

Oh, on my P71 doesn't have EGR ports behind the throttle body. Has anyone tackled cleaning them - ?under the elbow?

Yes I've cleaned 'under the elbow' three freakin times before I had the engine rebuilt. Always clogged up on me. Rather easy but make sure you have swivels with your socket set b/c it makes it much easier.

How did you get back there to clean out the ports? without disassembling I can see the process to getting in there.

What year car do you have??

The 91-95 4.6 (91 was Town Car only) have the all aluminum intake with the center mount throttle body





Pull off the elbow behind the throttle body no need to remove the throttle body itself



Now you see the passages the EGR gasses have to flow through. This car was not plugged, but my 94 Town Car was packed tight fully blocked. So the EGR opens but nothing flows into the intake, the DPFE will set a code after several drive cycles as it does not detect any flow.



For 96 up the Intake system was changed.



The EGR empties into a larger round hole 10mm? does not tend to clog up



Did not take any pics of my 96 plenum when it was off

Ok I've got the '94 crown Vic. I've had the check engine light for some time. Koeo error is insufficient flow. I've had knocking on acceleration and let it go for some time. Well, I started getting misfires worse and worse. Thought it may be the pfe since I only have one hose connection in mine. But first I stuck with the obvious. Time to change the plugs to new autolite platinums. The original was autolite copper. All 8 old plugs, while worn were burning normal and didn't show major issues I thought I would see. I am also leaking the valve stem seal. I thought I would see this in the plugs but didn't.

After the plugs I still had the hesitation so decided to clean the Egr channel. It was better than I thought. While being very careful with removing those bolts it took me about 2 hours or less. Once I got the throttle body off I saw just what those pictures show. Caked channel. I scraped the channel of course with a rag in the intake. Used compressed air to blow away all the debris. It took a while of careful scraping and the carbon pretty much flaked off. I carefully cleaned and reused the same gasket.

Put it all back together and it started fine. The knocking is also much less than before and acceleration is much better in the low rpm high torque. Stutter is almost all gone. Nothing like before. Check engine light hasn't come back on yet.

This is a very worthwhile task to clean this channel for all your older engines. If it doesn't clog for a year or two. I'm ok with that and will just clean it again, sooner than later. The more I drive it the less knock I hear. And the smoother this engine is running

One note. The carbon buildup was mostly around the holes, clogged, and the top of the gasket. The channel was probably 50% clogged with dried carbon soot. The square Egr hole was clear with little buildup there.