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1998 Forester S
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118 Posts
Discussion Starter · #1 ·
All,
I've been chasing this P0400 code for about a month now. Of course, my inspection ran up, as did the 10 day extension I received. Now its become fairly important to fix it. I wish I hadn't procrastinated when the light first came on :chair:

So, here's what I've done.

Replaced all vacuum lines associated (and some not associated) with the EGR system based on the Subaru EGR Diagram (I am friends with a manager at a Subaru dealer, so he and a tech there are also helping me with this).

Removed, inspected, and cleaned the EGR valve. It is functioning and clean now.

Replaced the steel lines associated with the EGR valve.

Replaced the BPT with a known good BPT

Replaced the sensors on the fender-well with known good units.

Replaced the filter that runs between the T and the sensor/switch on the fender-well.

Only other suggestion is to install an oil catch can, in case I'm getting a lot of blow by (engine has 220000mi on it) but the PCV and other breather tubes don't have an excessive amount oil in them. There was a lot of carbon deposits but we've confirmed that all paths are clean (vacuum testing and pressure testing after cleaning with SOA fuel injector cleaner). The tech has suggested that this is typically a long term solution, but more-so in high mileage turbo subaru's than the N/A Subarus... and even so, the CEL shouldn't return after the requisite two failed drive cycles after we cleaned it if everything was functioning correctly.

Is there anything we're missing? Should I just start throwing parts at it? I hate wasting money when we're using known-good parts.


Thanks in advance for any help. Everything I've done is everything I've found on this forum, Legacy forums, and other Impreza forums, as well as what SOA says in their '98 service manual.
 

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1998 Forester S
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118 Posts
Discussion Starter · #3 ·
Not a bad idea. I'll be tearing into it tonight and swapping the EGR valve with a known-good unit. Thats the only thing thats really left besides a wiring issue. Also going to zip-tie all of my vacuum connections and re-cut a few that might be a bit short to make sure there are no vacuum leaks.

The plus side is, the car runs almost like new now, and my gas mileage has gone up by a point or two. Now I just wish I could get it inspected :mob:
 

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1998 Forester S
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118 Posts
Discussion Starter · #5 ·
I used the endwrench article to get where I am so far. While I'm checking all the wiring harnesses, I'll test both my original, and the replacement EGR Solenoid (as described in the vcertt article) to see if that might help. Thanks for the links!
 

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01 Forester S
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102 Posts
You should be able to -see- the EGR valve flutter under throttle movement. At least you'll know it's good. Just reach over for the throttle bellcrank, watch the EGR shaft, and blip the throttle. You should be able to clearly see movement. If you manually push the EGR open, the engine should stumble a bit, and clear up when you let go. Can't recall, but you should replace all your vac lines here too, esp high mileage car.

Read the long articles. Very informative, if a bit much to digest. P0400s are a pain. :cool:
 

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1998 Forester S
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118 Posts
Discussion Starter · #7 ·
You should be able to -see- the EGR valve flutter under throttle movement. At least you'll know it's good. Just reach over for the throttle bellcrank, watch the EGR shaft, and blip the throttle. You should be able to clearly see movement. If you manually push the EGR open, the engine should stumble a bit, and clear up when you let go. Can't recall, but you should replace all your vac lines here too, esp high mileage car.

Read the long articles. Very informative, if a bit much to digest. P0400s are a pain. :cool:
Thanks, and they certainly are a pain! First thing I did was replace nearly every vacuum line in my engine bay. Then I replaced and pressure tested the three metal lines associated. One was plugged (the one that runs from the BPT to the intake). Thats now unplugged.

Also, my EGR valve was working but was sticky even after cleaning. I swapped on a new one when I checked the wiring (all good, btw). I reset the ECU and am doing my drive cycles now. If this doesn't work then I'll probably look to the two solenoids located just under/on the back side of the intake manifold. I didn't notice the wiring harness running to them until I was checking the wiring. The EGR valve that I put on (a known-good used) moves much smoother than my original one and the car doesn't stumble as much but still does, so I suspect that its possibly that solenoid. The test description is in the second document posted above. There are two - one on the drivers side and one on the passengers side. I was quoted $85 for the one on the drivers side and $60 for the one on the passenger side.

So, we'll see. All the known-good parts I've swapped are borrowed so hopefully I can get it inspected so I can give the parts back and take time to replace whats bad on mine without just throwing parts at it.

Thanks,
Eric
 

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1998 Forester S
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118 Posts
Discussion Starter · #8 ·
Just an FYI, the EGR valve fixed it. I swapped on a known good used unit and the CEL hasn't come back on in several thousand miles.
 

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2004 Forester XT 4EAT
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1,343 Posts
Yes, I am bumping a 11 year old thread to add the info I found on the Wayback Machine archive....copy the link, paste into the Wayback and hopefully you'll get a date.
See attached.

I"ll Clean > Replace my EGR as the BPT replacement didn't fix it this time (did on a '96 Legacy).
 

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