location of egr valve sensor on 2003 Mercury Grand Marquis

Check engine light came on, a new egr valve was replace after clearing the code vacuum is acceptable, car runs for a day but flashes a code again for in-sufficient egr. flow.what is the solution?

vacuum is acceptable??? how was it measured?? who diaged this??

anyway, if it is a 401 code, chances are it is a dpfe sensor. it is a common failure but needs to be confirmed by a shop with a scanner who can verify voltage changes.