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
Possible Solutions
With a P0402, it is common for people to replace the EGR valve, only to have the
problem return. The most likely solution is to replace the DPFE sensor.
* Check the voltage at the DPFE sensor both at idle and when the EGR is open
* Replace the DPFE sensor