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
You should look at a likely solution of replacing the DPFE sensor.
- Check the voltage at the DPFE sensor both at idle and when the EGR is open
- Replace the DPFE sensor