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Old 07-24-2017, 05:31 PM   #1
Luxkeiwoker
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Default Help troubleshooting P0448 (MY06 STI)

Hey guys,

I have had a CEL for the last couple of months and since I started to use the car more and more, it really started to annoy me, especially because cruise control is deactivated (blinking light).

I used my OBDLink LX to diagnose the code, and received

Code:
P0448 Evaporative Emission Control System Vent Valve/Solenoid Circuit Shorted
After deletion of the error, it popped back up after a few miles. I then started digging into possible root causes. Seems like it's the vent valve for the charocal canister.

Here is what I did so far (pictures below):

- inspection of the canister - looks fine
- took of the electrical plug of the valve and cleaned it from any debris/dirt
- put the car in test mode (2 green plugs under the steering column) and measured the voltage between both cables --> it was varying between ~7 to ~12 Volts which is presumably what it should do
- also checked if there is a shortage on the plug, but the voltmeter didn't beep
- measured the resistance between both connectors on the valve --> voltmeter shows ~27 Ohms (is that correct?)
- tried to remove the valve from the canister, but it sits in there pretty tight - not sure if it is even designed to be pulled out like that
- put the plug back on the valve actuator while in test mode to hear if there is any noise coming from the valve --> it stayed silent



I'm not sure what to conclude now. Is the valve defective? If so, can I replace it with a new one, or do I have to buy a completely new charocal can?

Since I'm based in Europe, I don't really care about the EVAP system, so if there is any way to just completely disable this while also not having a CEL, I'm open to it.
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Old 07-24-2017, 06:36 PM   #2
EJ_Enthusiast
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Did you check the input signal voltage at the ECM?
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Old 07-24-2017, 06:37 PM   #3
Charlie-III
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If it's anything like our 05 (likely), the housing on our vent valve was broken allowing air past the seal. We also had a silent valve when power was applied to it.
I bought a new valve from RockAuto for about $38US. Could not get hardware apart, so broke off the mounting tab and tywrapped the new valve in.
No more code, valve was replaced about a week ago.
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Old 07-24-2017, 06:39 PM   #4
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If you turn the ignition switch to the ON position and measure the voltage between ECM and a chassis ground. The connector on the ECM to test would be (B134) Number 13 (I believe that's the pin) and a chassis ground.
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Old 07-24-2017, 11:06 PM   #5
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Hopefully it's just a valve but if not I'm here to help if you'd like to go through diagnostic steps to eliminate possible culprits for your check engine light concern.
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Old 07-25-2017, 08:27 AM   #6
Luxkeiwoker
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Quote:
Originally Posted by EJ_Enthusiast View Post
Hopefully it's just a valve but if not I'm here to help if you'd like to go through diagnostic steps to eliminate possible culprits for your check engine light concern.
Thanks, I will measure directly on the ECM as soon as I'm back from vacation. Do you happen to know if the measured resistance of the valve (27 Ohm) is correct?

Can I remove the valve from the charocal can, or would I need to replace the complete can? I believe there is a difference between the 04/05 model and the 06/07 one. The P/N is different for the charocal can and so is the pricing (the latter model is much more expensive)
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Old 07-25-2017, 08:30 AM   #7
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I'm not sure if the valve can be separated (today is my day off and I'm a Subaru tech at a dealer) but otherwise I'd try to check for you. As for the ohm reading, if I remember correctly that reading may be too high (27 ohms seems out of spec). I'll look into it again and I'll get back to you.
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Old 08-11-2017, 05:27 PM   #8
Luxkeiwoker
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Ok so I measured the voltage at the ECM on the pin while in test mode (I confirmed it as well with the shop manual and it is indeed Pin 13). The voltage is cycling between 11,3 V (battery voltage) and 0 V. I then measured the voltage with the valve disconnected and nothing changed. Still cycling as it should. So the wirering seems to be OK.

I then hooked up the electrical connectors on the valve to my voltmeter and measured the resistance again. It showed ~ 32 Ohms.

Since I still couldn't hear or feel anything during test mode and the plug connected, I decided to hook up the valve directly to a voltage source (10V) by crocodile clips. When connecting the top pin to + and the lower pin - nothing happend. This seems to be the right polarity since the actual plug delivers the voltage to the pin on the top. I switched the power source on and off serveral times since I thought the the valve may just be stuck and could loosen up by quickly applying voltage and disconnecting it again

Oddly enough when I reversed the polarity I could hear a clicking noise which sounded and felt like a closing or opening relais but not like a mechanical valve.

I re-measured the resistance after that again and the voltmeter showed 4 Ohms and slowly rising.

So now what?
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Old 08-12-2017, 01:42 AM   #9
Charlie-III
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Sounds like a dead valve. It's a coil inside it, no polarity so it will work wired either way.

If you want to be sure, pull the hoses off, blow through the valve each direction. Then, apply power to the valve and blow through each way.
Should be obvious if the valve is working or not.

Ours could just replace the valve separate from the canister.
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