The EGR ports can get blocked after some time by hard black deposits.
The only way to clean the involved ports is to remove the EGR valve and
start scraping. A solvent might also be utilized. Depending on how bad
the deposits are... certain intake components may have to be removed.
But before you go through all that... you better run the error code and
see what it says...

Professor
www.telstar-electronics.com