Hi, Ive got a question for all you code readers out there. My dreaded check engine light has been on for about a month. I bought a code reader recently and checked it out. Two codes come up; PO401 and PO446. Can anybody tell me what these mean. My book says "Exhaust Gas Recirc. Flow Insufficient Detected" and " Evaporative Emission Control System Vent Control Circuit Malfunction". Huh? Can someone convert this to english for me. Which sensors, location on vehicle, etc..... this is a 97 5.4L Expedition. Im very grateful for any help.

Sportsman

 

There are several reasons this P0401 code can appear. I just fixed my 98 F150 4.6 L 112,000 Miles with the same code. It turned out to be the EGR Ports were clogged with carbon. Disconnect the vacuum hose from the ERG Valve and cap it. Then apply vacuum (outside source) to the ERG while the engine is idling. If it continues to run smoothly the ports are blocked. The engine should stumble or stall if the ports are clear. To clean them you will have to remove the throat from the manifold. The EGR Valve or the PDFE Switch could also be the problem. I'm not sure about the P0446 code

 

50th ann, thanks for your reply. I did a search for both these codes and came up with alot of info. for 401 and nothing for 446. Your right on track with 401. I pulled a vacuum off my egr and the engine almost died. So I went ahead and replaced the differential pressure sensor (dpfe) . Still need to take her for a drive and check for that code. the 446 is in the evap. system, so for now I replaced the gas cap. We'll see. Thanks again

Sportsman

 

Check for plugging downstream of the EGR valve. This picture shows just how bad it can be. Both me (98 expedition) 110k and my brother in law (98 F150) had same problem. Codes showed low EGR flow. Tried all the suggestions first, bought new DPFE switches, Cleaned EGR valve and exhaust manifold tube, etc. All the time it was this simple ugly plugging. Relative easy to clean after removing throttle body.

A business card is inserted in TB so you can see black sludge ball. There are two one for each port and there shadows on the card. Passage ways totally plugged. Used coat hanger to clean.

 

AggieMike, thanks for the picture. Very helpful. I replaced the differential pressure feedback sensor and still havent recieved the po401 code. but, I still have the po446 code. Living with it for now, but I'll probably end up taking it into the shop to get rid of that pita light. Thanks again.

Sportsman

 

There are a couple of common things I've seen that cause the P0446. The code means there is a problem with the EVAP system which includes the canister which is above and behind the rear axle.
These are in the order I would check them.
Do you have a lot of dirt/mud where you are? The EVAP system can get plugged with dirt.
I've also seen quite a few with the wiring that goes to the cansister purge solenoid ripped off. The solenoid is at the front of the canister.
I've seen the wiring corrode where it goes into the solenoid and I've seen bad solenoids too.

 

On my 06 F150 I can not get the code P0446 to clear out.it keeps coming back right away. Ive changed the CVS, confirmed purge valve is working, correct voltage at the CVS, no broken wired all the way to the PCM. I NEED HELP!! i have to get it cleared to pass inspection for emissions test and plates are expired now!!

 

The 446 code tells you it is a 'Vent' control circuit malfunction on the EVAP system.
Good luck.

 

Any ideas? I've traced everything and tested everything and tried everything i've found on these threads. I keep hearing that replacing the PCM is the only thing left but theres gotta be something else?

 

Clifford,

Please make your own NEW thread in the correct section of the forum instead of hijacking an unrelated discussion in the wrong section.