Merc C Class 220 Cdi dtc code

[T1pper]

My brother has a Merc C 220 sport 2006, it keeps putting up a fault code of P0404 which is EGR related.
He has changed the EGR valve and the MAF sensor, any ideas what the fault maybe??
Its a well serviced 100k mile car owned from new and have not had any other problems.
Thanks in advance

[melhookv12]

Wiring fault? Bad connection. Have you Google it. There is a minefield of info on Google. Sometimes helps,sometimes hinders.

[Elliot2000]

Is it a vacuum operated egr valve? If so have u checked thaw solenoid valve

[T1pper]

Thanks for the replies,the woring seems to be in good original order,I have Googled the fault code and it states egr out of range or performance but very little on how to fix the problem.
lastly there is a vacuum valve on the sustem I have checked the pipework and visually the valve is operating.
Any other ideas??