Subaru Problems? Ask a Mechanic for Answers ASAP
If you look at the engine you should see a round plastic disk looking item. This is the BPD valve. It regulates some of the vacuum to the egr. If you pull it off and tap it on your hand you might get some water out of the bottom hose. If you do, replace it. This is the most common cause of the 400 code on these.
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