Hi There, Ive got a '99 Outback and a '95 Legacy Wagon. Both throwing P0400 codes. Tested both EGR valves, cleaned them, and both hold vacuum. Cleaned out different tubes in the EGR system, and still getting the 400 code.

Then tested both solenoids and they both actuate when given power. Tested the plug and the plug gives 12 volts.

My specific question is about a vacuum test - the solenoid has 2 vacuum ports and when I blew thru them without power, one let air thru and the other port did not.

Is this supposed to happen? Or are they both supposed to be closed? Just wanted to make sure this is my issue before buying the part as they are $100 each. Here is a link to the part on Ebay: https://ebay.us/m/PihAzZ

Additional detailed question that you can answer or not. The initial code came from the '99, and my '95 did not have a code at the time. So I put the EGR VALVE from the 95 onto the 99 to see if the VALVE was the issue, but the code came back. I think I may have also put the VALVE from the 99 on the 95 and then, to my memory, the 95 then threw the 400 code as well. So I may have caused an issue there. If that helps you diagnose this, great, if not, my main question is about the vacuum.

Thanks for the help!

FWIW:  I replaced the BPT - back pressure transducer - that sits on top of the EGR valve and has 4 vacuum lines connected to fix my p0400. These are readily avl. on most EGR subarus from the '90s and Toyotas - I used a  (used) Toyota version on my '96 Legacy w/the 2.2. 

Edited November 13, 2025Nov 13 by wtdash