TboneH

My truck has been to the mechanic no less than 5 times in the last two weeks over a seemingly innocuous trouble code: P0401 - EGR insufficient flow. The first thing he did was replace the DPFE sensor. This allows the truck to go for about 50 miles before the code pops back up again and the sensor has seemingly gone bad. He has also tested exhaust back pressure and thoroughly cleaned and tested the EGR valve itself, among other things. He now believes that the root of the issue is excessive water in the DPFE sensor.

From my research, I've read that water in the sensor is fairly normal, and while it does cause corrosion, the sensor should last for quite a while, certainly more than 50 miles. I should also mention that in the past, I got a catalytic converter trouble code (don't remember which one, sorry!) as a result of a misfiring cylinder, which went away on its own after resolving the misfire. Is there any way the cat could still be causing problems even if the backpressure reading is fine? I'm a bit lost on this stuff to be honest, but I'm trying to do what I can to help my mechanic out. Does anyone here have experience with something like this/EGR issues in general?

Jbrew

Do you know the year and engine ? Might bring it back to the shop if your clueless..they can tell you.

white89gt

Sounds like the mechanic is clueless. I'd go to another shop, honestly.

Fixitman

Sounds to me like your EGR ports in the throttle body are clogged. A common problem. I chased this one for some time until I found cure. Throttle body comes off for a good cleaning. Ports from EGR to throttle body especially. Also I would consider a different mechanic. This has been common on high mileage 4.6L and maybe the 5.4. Good luck.

TboneH

It's a 2000, 5.4L. I'm not completely ignorant, I just don't have much experience diagnosing problems. Fixitman, thanks for the suggestion, I'll pass that one on to my mechanic. As for finding a new mechanic, it's crossed my mind, but it's a bit too late for this one. I'd prefer not to pay two people for one job.

Edit: I asked about the throttle body ports, they have been checked. Had some light carbon build up, but that's all. Any other ideas?

Jbrew

Yea , but we were until you told us. The crystal ball wasn't kicking out your model year or engine...on the fritz again.

That's not an issue with the 5four engines, soley a 4six problem.

For the 5four I would suck test it. This will determine whether the diaphragm is good or compromised. An exhaust leak in the EGR tube or close to it can also forward a 401 DTC.

Also look here for diagrams and good troubleshooting info, -

Scroll down for 401, -

http://www.fordscorpio.co.uk/egrmonitor.htm