I need help guys,
My wifes check engine light is on and the repair shop says it is throwing an 0400 error. He says that it is an EGR malfunction. What do I do and how do I fix it? The car is a 2001 Mazda Millenia (not an S).
Thanks

 

Very common problem on that engine with the EGR passages getting clogged up with carbon. Also the vacuum sensing line to the boost sensor gets restricted up as well where the line connect up to the intake manifold. You will probably want to start by seeing if you are getting a good strong vacuum signal up to the EGR Boost sensor solenoid valve. Will post up a pic below of the sensor and valve location. It is #12 in the drawing. The solenoid should look like the ones in the picture at bottom of this thread link.
https://www.mazdaforum.com/m_10328/tm.htm
The solenoid you are looking to locate has two electrical wires to it colored White w/ green stripe and Red with Black stripe.
Two vacuum lines on this solenoid. One should go to the boost sensor which is right next to it and is often labeled as such, the other line goes to the intake manifold. With engine idling. Remove the line from the manifold and make sure you have good strong vacuum. Reconnect that liine and then remove the other one that goes to the boost sensor. Should not have any vacuum at all. Post back up with the results you have found.
[IMG]local://upfiles/1377/371474F8C0D843DB83D57A583EB10C98.gif[/IMG]

 

indeed, very common in the 95-98 years, just clean it out and your good to go