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I have a '96 Subaru Legacy Outback(Wagon), automatic transmission, 2.5L engine. I've had the P0400 code being thrown for about 2 1/2 months now. Cleaned and tested EGR valve, and that's properly functioning. I checked the vacuum lines and they're all good as well. From what I've read, this is a fairly common problem with Gen.1 Subaru cars. Any other suggestions for me? Driving to and from Bethlehem from Quakertown every day for school is killing me on gas with the code having defaulted the fuel mixture now. Also, could this have any relation to loss of braking pressure? Thanks in advance! Any and all help is appreciated!
 

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95 Legacy EJ22 5MT, 98 Legacy EJ22 5MT, 99 Legacy Outback EJ25 4EAT "Agent 99", 01 Forester EJ25 4EAT
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I have nothing but Gen 1 cars and have never had to deal with this code (or any other vacuum-related problem that wasn't actually just me confusing myself), but you're new here and should get some answer because this is an amazingly helpful joint. So without directly addressing your P0400/EGR problem...

When you say "checked the vacuum lines", does that mean you just did a visual, or did you actually put a vacuum gauge on the manifold? I ask because brake boost is also driven by manifold vacuum, so if you've got a significant leak it could well manifest as a loss of braking pressure in addition to the sensor complaint.
 

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2007 2.5 L Obsidian Black Outback XTL
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Maybe the problem is more subtle than just being a bad valve. P0400 indicates "no flow" from the EGR system... Maybe something is obstructed.

A couple of quick checks.

Clean out the hose and tubing between the EGR valve and the intake manifold. Carbon could be plugging it.
Remove the EGR valve and start the car.. you should immediately know from the plume of exhaust gas billowing out of the EGR flange if there was an obstruction before the valve
When you cleaned the valve did you test it? Using an ohmmeter there is an electrical solenoid coil that you will sense by the electrical resistance being a few ohms... You can put 12 volts across the coil and you should be able to see/hear the valve clacking open and closed.
 
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