Kept getting a code po401

the EGR should be somewhere on your exhaust manifold

Code 401 is for low EGR air flow. The EGR valve allows exhaust gas to be recirculated back thru the intake and reburned.
The problem could be the EGR valve, the sensor, or a blocked line.

A code P0401 most likely means one or more of the following has happened:

• The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
• There is a blockage in the EGR (tube), most likely carbon buildup
• The EGR valve is faulty
• The EGR valve may not be opening due to a lack of vaccuum

Possible SolutionsIn fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.

• Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
• Clean out the EGR valve and/or tubing to remove deposits
• Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
• Replace the DPFE sensor (with a good quality / OEM one)
• Replace the EGR valve

PO401: EGR insufficient flow detected
PO402: EGR excessive flow detected

A code P0402 most likely means one or more of the following has happened:

The DPFE (differential pressure) sensor is faulty and needs to be replaced
There is a blockage in the EGR (most likely carbon buildup)
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

Well, the po401 is saying is that the egr valve has restricted flow. After changing the egr and the tube, something else is causing the restriction. a more thorough diagnosis is recommended. The po420 code sounds like a possible catalyst failure or an o2 sensor failure.

I believe this code is insufficient EGR flow. On this engine, the passages to the EGR valve often become carboned up and cause this code. Remove the EGR valve and inspect the passages to see if they need to be cleaned.

Does the egr vavle open ? You will need to use a scanner to test the dpfe voltage when the egr valve is energized you should read around 3.5 4.00 volts. Also you could remove the vacume line from the egr valve and with the engine running you should see around 100 rpm drop in engine rpm at least this would indicate the egr valve is capable of flowing egr gases through the system to the cylinders.

PO401 Insufficient EGR Flow, valve could be stuck or disconected.

It could very possibly the EGR tubes are clogged or the EGR is not opening or could be DPFE; first i would check the tubes on the DPFE and also clean the EGR tubes and egr it self simple brake clean and a hanger can clean the tubes and spray some in the EGR it also can get gunked up and not move properly.

Hope this help to solve it (remember comment and rated this).

PO401 code means that:
The PCM has determined that there is insufficient flow in the exhaust gas recirculation system. Definition: EGR system fault (Exhaust Gas Recirculation) Probable Causes: a. Blocked passage on EGR system b. Failed EGR Valve c. EGR solenoid faulty d. Failed EGR pressure sensor where applicable e. Failed EGR position sensor where applicable

Clean the EGR air passage tube.

Carbon built up is worst inside this air passage tube.

You will need Seafoam or WD-40 and LOT OF TIME to clean out this tube.

A vacuum will help speed up the cleaning.


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