P0401 Insufficient EGR Flow

Description and meaning of DTC p0401

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/model. EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissionssystem, and is used to reduce combustion temperature and pressure to controlOxides of Nitrogen. There are generally three parts to the EGR system: the EGRvalve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation basedon engine temperature, load, etc. The P0401 code means that OBD detected aninsufficient amount of EGR.

p0401 diagnostic trouble code symptoms

You may notice drivability problems such as pinging (a. k. a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.

DTC p0401 - possible causes

A code P0401 most likely means one or more of the following has happened:The DPFE (differential pressure feedback EGR) sensor is faulty and needsto be replacedThere is a blockage in the EGR (tube), most likely carbon buildupThe EGR valve is faultyThe EGR valve may not be opening due to a lack of vaccuum

How to fix OBD-II diagnostic trouble code p0401

In 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 theEGR open Clean out the EGR valve and/or tubing to remove depositsCheck the voltage at the DPFE, compare to specified values (refer to a repairmanual for your specific model)Replace the DPFE sensor (with a good quality / OEM one)Replace the EGR valveRelated EGR codes: P0400, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409

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