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P0401 code !!!!!!!!!!

Old 05-26-2009, 09:47 PM
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Join Date: Feb 2009
Location: United States
Posts: 18
Unhappy P0401 code !!!!!!!!!!

2000 mountaineer v8 AWD
My check engine light came on, so I check the code and it gavve me a P0401, how should I tactle this code?
Old 05-27-2009, 01:15 AM
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Join Date: Nov 2008
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Posts: 232

That should be the code for insufficient EGR flow I believe... To really get into this one you may end up needing a scan tool but the simple checks would be to make sure the vacumline to the EGR valve is connected and not broken anywhere..

There is also a sendor that monitors the EGR flow (and in general this sensor is usually the problem).. This is mounted on the upper intake, should be a rectangular silver box with 2 hoses and a plug.. Make sure the two hoses are connected and not broken on each end... May also pay to remove them and make sure they are clear by blowing through them..

A crude test to see if the egr valve is flowing would be to disconnect the vac line to the valve and apply some variety of vaccum to the valve with the engine idling.. If it flows, the engine will idle really rough and may even stall.. Either a hand held vac pump is needed, or else attach a lenght of vac hose to the valve and suck on it (LOL crude but it works) If it no difference can be noticed with vaccum on the valve either it or the plumbing to/from it is plugged.. This will require removing the valve and cleaning the port in the intake and the valve itself...

The vac line that goes to the valve will lead to a solenoid that controls it.. Should be a sort of round black plastic piece with 2 vac lines and a 2 wire plug mounted near the egr valve istelf.... Disconnect the line that doesn't go to the valve and verify thatr you have suction there with the engine idiling... If no vac inspect the line for kinks or leaks..

To test the solenoid itself first check that you have battery voltage on the light blue orange wire to the solenoid with the key on.. If no power check fuse #13 in the box under the hood (15a).. IF power is there jump the brown pink wire to ground, you shoudl be able to feel the solenoid click.. WIth this grounded start the engine and check for suction at the line going to the egr.. (This could also be used to apply vac to the egr valve as mentioned earlier) If no vac is present but the hoses check out okay the solenoid is the culprit..

IF all of the above check out okay then it is most likely the egr pressure feedback sensor (the silver box with the 2 hoses and plug).. There are more involved tests to verify this but a scan tool capable of displaying serial data and initiating both a key on engine off, and key on engine running test is required...
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