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A code P0402 most likely means one or more of the following has
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
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.
What does that mean? EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE).
These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.
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.
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 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 Solutions 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 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
Re-Check the possible solutions and tell us news (remember 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)
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