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Discussion Starter #1 (Edited)
Hi,

My car will have 10 years next month! :eek: Has 98,456 KM on it only but I still have to repair a few things that breaks (so far, normal usage).

Anyways, the only thing I do on IWSTI is lurk and write how-to's. Since most of you guys moved to better cars (2009+) I'm still "stuck" with my old 2004 STi.

Let's begin before I get emotional here :p

So you are getting a P0457 code on your subaru. That's great. This means that something, somewhere in the wonderful emission process of your car, there's something wrong. Pretty broad statement? I thought so too.

Before you start, eliminated the obvious:

Did you change these parts lately:
-Air Intake
-turbo inlet pipe
-fuel pump

Air intake and turbo inlet pipe:
There is a known issue that the blue T connected, next to the alternator, will be disconnected. Check that first before going any further.

Fuel pump:
If you have replaced the fuel pump, did you re-seated or change the gasket? This is another common cause of this particular code.

Tools needed:
-Voltmeter
-Ratchet with 12MM socket
-Shrink tube
-Solder
-Extra wires
-Your head!
-The FSM 2004 Subaru Impreza WRX STi
Troubleshooting process:

First thing is to check that all the solenoid and valve are working and getting their proper voltage.

Here's the diagram for the emission process on the car:



Connector the green connectors. These are located under the steering wheel. Look up, they are sometimes hard to reach. Having these connected will make your car "power cycle" all the different electronic parts of the car. You can easily identify a bad part if it doesn't make a sound, or "click".



Turn the key position to ON. You will hear your car cycle away with all the clicks noises happening :)

Let's start to check if it's a purge control solenoid valve problem:
http://customcdr.com/images/purgesolenoid.jpg

Locate this near the blue T fitting previously identified and you will see the solenoid. Put your finger on it. Can you feel it clicking? Probably not your problem. Can't hear it click? Test the power with your voltmeter:


If you are reading around ~11v then the currant is fine. So there is power but the valve isen't operating. Get a new valve ;)

Jack the back of the car, move to the rear-passenger wheel. Locate this funny little box:


Unbolt all 3 x 12mm bolts.

Locate the Drain valve, also called the canister vent valve (part #42084FA120), can you feel it click? For, that was a no go. That ended up being the problem since the currant to the valve was good (was reading a solid 11v with the voltmeter.)

If you are not reading any currant, then the problem is in the wire. Split open the black tube and follow the wires, you should see the faulty wires due to corrotion. Replace the wires as needed.

More to come ...
 

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Discussion Starter #2
I'm sorry, i'm a bit busy lately so i'll be updating the last portion to include more pictures and how to test the different solenoid.
 

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Thanks for sharing.

You may want to include the conditions that cause the code, and the conditions the ECU needs before conduting the test. Is this a code that can be set with a loose gas cap?

Looking forward to the rest.
 

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I have this code on my car, I check the blue t connector, and it was connected, but I'm not sure if it's perfectly working. I changed my fuel pump last year, and the code kept showing up frequently, and now everytime after filling the gas. The gas pump frequently stopped while pumping, and I recently replaced the charcoal canister and thought the problem was fixed. However, it the code re-appeared after driving it on the freeway while on the cruise control.
I'm not sure if I have to replace the gas cap now or if anything else is causing this problem.
 

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Discussion Starter #5
Thanks Vanishing Point. Will do.

Subimp6u08: I had the same problem as you, it was a bad drain valve (#F42084FA120). This valve pressurised the gaz tank circuit and it indicate if the pressure if good or not. If the valve fails to close, then the ECU will throw a P0457 code. Test that valve, located on top of the charcoal canister, and see if it "clicks". That might be the culprit :)
 

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subscribed for use later. Thanks for your insight! =D did the vid ever come together??

I seem to only throw p0457 when I hit the 1/4 tank mark... is that strange? if I gas up before 1/4 tank, the code never comes up!
 

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I will also subscribe.

I recently had to rebuild my power steering pump, and in doing so I had to move the blue tee fitting and all that goes with it to access the back of the pump. Now the tee is all good but the little "U" shaped hose broke as it was brittle, so I replaced the hose and tee. I put in a brass tee with all three inputs being the same size, I could not find that small of a size hose at the time.

My question is will that cause any issues since the blue tee has as one small input and 2 bigger inputs? I did this since it was Sunday and I needed my car for work the next day.
 

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Just wondering if you ever finished this or made the video. I am getting the code as well. Replaced the valve and still there. Looks like I get it around 1/4 tank as well. Lol 04 sti here, dont see many around any more, sadly.

Sorry to bump this old thread but it was very helpful so far troubleshooting this issue.
 

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Although I think I am the only one in the world that still has an 04 sti, I thought I would give you an update for completeness. Closer inspection of the blue T connector revealed the bottom part was disconnected and the little connector from the small hose to the larger one was broken. Bought the assembly from subaru and replaced it.

One thing I wanted to point out, however, is I have been having slight stuttering at WOT for a while. I figured my motor was messed up or ECU was pulling timing or something. After I fixed the hose, no more stutter and running like new again!

I read somewhere evap system issues can cause stuttering and at least in my case this was true. HUGE relief!
 
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