Have replaced evr, egr, and dpfe. Still throwing this code.
Have cleared the lines to the dpfe and the hard line from
egr to manifold. Can pull vacuum manually on egr and engine
gets rough. Have 18 in-hg of vac to the evr. NO vac on the egr
side of the evr. Have checked vac with engine running
and plugging and unplugging the electrical connector.
Does this code have to be cleared or will it clear once the
problem is repaired. I'm tired of having to drive 50- 100
miles only to have the light come back when the sensor
tries to go ready to test. Where else do I need to look?
Need to have it inspected, but they won't touch it with
the cel lit or sensors not ready to test. Help!

 

For me, it WAS the DPFE.Just a guess, but do you hav a vacuum leak somewhere? It's cheap enough to replace the vacuum lines to/from the DPFE. A leak can throw this code I believe.

Tim
2001 Expedition

 

There is some groove at the base of the throttle body that cruds up and this causes an EGR problem. I don't know the exact details. It has been discussed on the board before. Try a search.

 

Pulled those lines and run compressed air through them.
They appear to be in good shape, no cracks or signs of
dry rot. Made sure they were routed right. I'm working
from the Hayes manual. I guess my real question is at
what point should I see vacuum at the egr. I've checked
voltages at the evr and dpfe. The resistance of the the
evr is within spec. Bypassing the evr only opens the egr
wide open. I also put a new vac line from evr to egr to
check the factory line. Everything checks out, but never
any vac to the egr.

A little backround on the truck. I added an Airaid intake
and run open duel pipes from the cats out. It has a rumble
but baffle tips took the edge off. Thats all for performance
mods. I did have trouble with the vacuum line that connects
the pvc valve to the hard line. It was collapsing, but some re-enforced fuel line corrected that.

 

Thanks roadie,

I'll give it a look.

 

It does help if you identify your vehicle by year, engine, and transmission. There are differences and the lack of correct identification makes it just guesswork as to what reference material is to be used.

The EVR should only open and supply vacuum to the EGR during those periods of time when the computer commands it. The best time would be while cruising down the road with a fully-warmed up engine. Obviously, you will need a T and a long piece of hose to accomplish this. You cannot do this at idle unless your scanner has the capability of running the KOER portion of the PCM Quick Test.

Monitor the output signal voltage of the DPFE sensor while pulling that vacuum on the EGR valve. If there is adequate EGR flow (ports not clogged), and the DPFE is connected and working properly, you should see the voltage rise from around 1 Volt DC up towards 4-5 VDC as the vacuum to the EGR is increased. It is very possible that there is partial blockage of the EGR ports so that, while application of vacuum to the EGR valve will cause the engine to stumble during your self-test, the amount of EGR flow measured during the PCM EGR Monitor cyle is less than what is expected. This will trigger the P0401 code as will a gross failure of many of the other components of the EGR subsystem.

Best suggestion has already been made by Roadie. Check what he suggested.

Steve

 

Sorry I thought I had all that in my profile. It has been fixed.
Thanks for pointing it out SHO89.

Engine - 4.6L
Tranny - auto 4 speed/w overdrive

 

Thanks for the input. Pulled the throttle body
and the ports were completely blocked. 30 minutes of
chipping and reaming and the problem seems to be
cured. I would advise anyone who gets an emission
code involving EGR to pull the throttle body first. It's
only 5 bucks for a gasket. I've got close to 200 in parts
trying to shotgun this problem. The upside is I have a new
EGR system. The carbon build-up is probably made worse
by running cheap fuel. Try to run some good stuff once in
a while.

 

Code P 0401 does say insufficient flow! A blockage would do that.