What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
EGR stands for Exhaust Gas Recirculation. It is part of the vehicle’s emissions system and is used to reduce combustion temperature and pressure to control nitrogen oxides. The EGR system typically includes three components: the EGR valve, an actuator solenoid, and an EGR differential pressure sensor (DPFE). These elements work together to provide the correct amount of recirculation based on engine temperature, load, etc. Code P0401 means the OBD has detected an insufficient amount of EGR flow.
Symptoms
You may notice driving issues such as engine knocking (i.e., pre-ignition, pinging) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.
Causes
A P0401 code most likely means one or more of the following events has occurred
- The DPFE (EGR) sensor is faulty and needs replacement
- There is a blockage in the EGR (tube), most likely carbon buildup
- The EGR valve is defective
- The EGR valve may not open due to lack of vacuum
Possible Solutions
When fixing this code, it’s quite common for people to simply replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.
Use a vacuum pump and open the EGR valve while monitoring engine RPM and DPFE voltage. There should be a noticeable difference in RPM with the EGR open
Clean the EGR valve and/or tube to remove deposits
Check voltage at the DPFE, compare it to specified values (refer to a repair manual for your specific model)
Replace the DPFE sensor (with a high-quality/OEM sensor)
Replace the EGR valve
Related EGR codes: P0400, P0402, P0403, P0404, P0405, P0406, P0407, P0408, P0409