You should start with a VCDS check. On other boards, fixes have been severed wires between the EGR valve and ECU, and replacement of the EGR valve (not including EGR cooler). Check wiring first, I guess. Has the EGR system been redone since new? I replaced the cooler and valve last winter - chose to fix it rather than delete which would have thrown a check engine light which causes a DriveClean fail. Not cheap fix - but my cooler was hissing, and I figure I'm good now for the life of the car (just redid timing belt for the second time w new cam this time). Still a lot cheaper than replacing the car!