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1998 - P0400 - Exhaust Gas Recirculation Flow?

24951 Views 6 Replies 7 Participants Last post by  Bovka
P0400--Exhaust Gas Recirculation Flow---HELP

How do I take care of it...killed the engine check light 5 times already.
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I checked my 99-02 Forester Manual and it has no info on EGR system. Must have dropped it after 98.

P0400 is EGR system flow malfunction. I could not find a detailed explanation but usually, the engine control system detects inadequate flow by attempting to lean mixture w/ EGR dilution (opening EGR valve). If it can't detect leaning, the EGR flow is inadequate and code is set.

Why lack of flow? It can be blocked EGR valve (carbon deposits), blocked EGR passage, or loss of EGR valve drive (vacuum line leak if valve is vacuum actuated). Vacuum is supplied through an electrical solenoid valve controled by ECM. If vacuum solenoid valve is bad, a different code is usually set for this component.

Check EGR system for integrity; vacuum lines, EGR solenoid valve works, no wiring defects.

Remove EGR valve and inspect valve movement and openings for blockages, damage.

Inspect EGR passages (if accessible for clear flow path). In some vehicles, you can "rod out" the EGR passages, but I don't know about yours.

good luck
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The EGR valve did have a problem one time and the engine check light came on stating that the EGR valve was bad...I took it off and it was clogged with frozen water or deposite, repalced the EGR valve with a different one and delete the code. Then this code came on about 1 month after...

You are write about vaccum being controled by an electrical signal...

I will check the vaccum lines and the EGR again today when I get home...I will update the post when I get the results.

the same problem

here is a link that my further help you...are you ready to see how far this rabbit hole goes?
ugh i can't post a link yet until after 15 post or more so i better get posting but my previous post is under this thread and its called po400 with hard shifting

to begin I work at a local parts store as an assistant manager and i've been working on vehicles since i was 12 so i've got a lot of trouble shooting knowledge or enough to get me in trouble but heres what i just found out.

at the last post i was still unsure about my codes and my knowledge is that the egr valve can get deposits on it sure. but it porbably isnt bad....heres the test for that, start your car and manually operate the valve with your finger and see if the engine stumbles maybe it might stall..which is a good sign to you that you do not need to take out the egr valve or tube to clean. next you can buy some small inexpensive hosing that fits on the EGR valve fitting i dont remember the size of the top of my head but attach a length of the tubing to the egr valve itself and suck on the other end of the tube watching the egr actuate. suck as hard as you can and hold it and see if the valve falls at all (that could mean a small vacuum leak in the valve itself. ) if thats okay and no valve falling occurs then onto the next area. i've heard that the hoses right off of the intake leak and also the metal tubes as well. so like i did was a systematic plug and suck and wait to see if any substantial vacuum leak is i know that sounds funny but it does i do own a vacuum gauge and a vacuum hand pump to do this instead and to be more here are my new findings after tonights tests. i systematically tested from the intake to the EGR valve with the vacuum gauge and vacuum pump and this is what i found....
I got about 5 to 10 in Mg per hose before the back pressure transducer (BPT) looks like a flying space ship thingy. after the BPT there is one hose going to the EGR solenoid this hose at about 10-20ish in Mg depending on where the acceleration was....this is where i wanted to test mine
i wanted to know if the EGR solenoid was even cycling right at all i connected my vacuum gauge in line after the EGR solenoid and ran the tube in side the car through the firewall and went for a drive. this is with a warm operating temp car. Remember the EGR solenoid is operated from many things the transmission control module being one of them so speed has a thing to do with this. I went from went from 0-45mph normal acceleration with the EGR opened from 0-35mph after 35 mph no cycling at all occured. I even decided to try on the highway. (I know this is a lot but i've researched a lot and i'm a nerd on top of it) to step back a bit the po400 code is thrown only when certain conditions are met meaning 50-55mph and temps are just right plus two different trips under same conditions will the computer run the flow diags which is gathered from a mirad of sensors i.e. oxygen, speed, pressure sensor, etc. since there is no real electrical connection on the EGR valve itself to measure flow is how the computer thinks if it needs to throw the code. well here is my interesting finding of the night after all of this explanation. while driving i noticed that my pressure gauge was only going to about 5-10 in Mg however i knew that right before the EGR solenoid i was getting almost double that. well I decided to test just the EGR solenoid I removed from the solenoid from the engine and made a tester from small speaker type connecters and some wire connecting them to the terminals of the EGR solenoid. taking the other free ends i was going to touch them to the battery directly. now i applied a vacuum with my pump at 30 in Mg at the further most hole on the solenoid, the middle hole i attached my vacuum gauge reading 0 in Mg and then i touched the wires to the battery actuating the solenoid (a click sound was heard which then i knew the solenoid was now open) still with vacuum pump attached and pressure gauge i watched as a direct drop in pressure resulted from 30 in Mg to about 10 in Mg and then slowly dropped to 0 in Mg. i disconnected the solenoid from the battery and tried again this time applying as much vacuum as a could to the solenoid almost 40 in Mg no leaking, 0 in Mg at pressure guage..touched wires to battery and click noise heard. pressure sensed at guage now went from 40 in Mg to a sudden 20 in Mg and slowly leaked to 0 in Mg. so i am wondering if i found the leak in the solenoid... my thinking is that i get almost a steady 20-25 in Mg from the engine after BPT and before the solenoid. yet it seems after the solenoid before the EGR valve i have almost half of what i had which seems very weak. and heres the sticker...i also tried this on the pressure sensing solenoid on the passenger strut tower and found their to be an instant leak across the solenoid. the pressure sensing solenoid is also hooked up to the transmission control module which changes the operation of tranny shifting and EGR solenoid cycling. thus I think i found my bug with my po400 code. remember this is a conditional code not a part specific code. mainly b/c its not exactly something electrical you are working with. I mean both my solenoids operate fine clicking and allowing vacuum to pass through however theres again no way for the engine to measure direct vacuum pressure so if the solenoid operates the computer thinks its fine. however it could still be leaking. or your BPT could be bad. or you have a vacuum leak in a hose. i went ahead and took the liberty and replaced all of my vacuum hoses. its tricky and time consuming...i've read nothing but heart ache and lots of money thrown at this code for it to still come back on...I even talked with a seasoned SUbaru tech and told me right away that it was my BPT however mine seems to work just fine so even the experts dont always it looks like my fix is going to be around $70 maybe less maybe more for a new EGR solenoid. I still want to verify my theory on a solenoid from work then i'll feel more better in my prognosis and ultimately money leaving my wallet.
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i'm not going to even attempt to read that, holy crap.
its good stuff

hey its the answer to the p0400 code issue it should be read....
Hi everyone, I'm having an exact error code . can someone please show me a diagram of EGR System. I only know the EGR valve itself and cleaned it but the code come back after a while. i would like to clean the hoses, pipes etc if i know where they are. my car is 2009 Forester 2.0 japanese version and EGR valve is attached in front of the engine just behind alternator. Thanks:thumbsup:


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