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Old 01-30-2006, 10:27 AM   #1
SeaRex
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Default PO456 evap code / gas cap question

Per Subaru, the CEL in my car (120k 2.0 WRX wagon) is PO456, gas cap not too tight.

Well, I always give the gas cap 10 clicks when tightening it (or more, never fewer). And, the CEL came on 200 miles into a tank of gas.

Any thoughts on what else, other than an undertightened gas cap might cause this?

Cheers,

Sean
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Old 01-30-2006, 10:32 AM   #2
Mulder
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There may be a leak elsewhere in the evaporative system, the hoses and other parts should be checked. Also it's possible that the seal on the gas cap is worn and no longer holding pressure.
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Old 01-30-2006, 10:43 AM   #3
SeaRex
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Quote:
Originally Posted by Mulder
There may be a leak elsewhere in the evaporative system, the hoses and other parts should be checked. Also it's possible that the seal on the gas cap is worn and no longer holding pressure.
Thanks.

I explained to the dealership how anal I was about tightening the gas cap and about how the CEL happened 200 miles into a tank of gas (and 40 miles into a 75-mile trip) but over the phone I could sense the eyeroll. They said they'd look for "spider webs," at which point I thanked them for their time and asked how much longer they'd have the car.

My code is a PO456. According to the list on NASIOC, 457 is listed as the gas cap issue -- are these really one in the same?

Cheers,

Sean
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Old 01-30-2006, 11:03 AM   #4
solbey11
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Well you can't really expect the dealership to diagnose your car over the phone. If it's that much of an issue for you, then just take your car in and let them look at it.

But like Mulder said, check your evap system over really well. It's a system to keep fuel vapors from being released into the atmosphere. Therefore, it has hoses running from the fuel tank to your evap canister to your engine compartment. The best place to start would be inside the rear bumper where the evap canister is. There are rubber lines that go into it and come out of it. Check to make sure none of them are loose or cracked. Then look over the canister to make sure it isn't cracked. Also look at the seal on your fuel cap as well to make sure it isn't torn. In my opinion, 10 clicks is really overdoing it. Once it clicks 3-4 times, it's tight.
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Old 01-30-2006, 11:11 AM   #5
solbey11
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I looked into it a little more and...
P0456 Evaporative emission control system malfunction
It's a very general code, so it could be anything from a loose hose, faulty gas cap, all the way to a faulty drain valve or purge control solenoid valve. So unless you know what you are looking for, it would be better for you to just take it to the dealership and have it looked at.
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Old 01-30-2006, 11:13 AM   #6
SeaRex
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Quote:
Originally Posted by solbey11
Well you can't really expect the dealership to diagnose your car over the phone. If it's that much of an issue for you, then just take your car in and let them look at it.

But like Mulder said, check your evap system over really well. It's a system to keep fuel vapors from being released into the atmosphere. Therefore, it has hoses running from the fuel tank to your evap canister to your engine compartment. The best place to start would be inside the rear bumper where the evap canister is. There are rubber lines that go into it and come out of it. Check to make sure none of them are loose or cracked. Then look over the canister to make sure it isn't cracked. Also look at the seal on your fuel cap as well to make sure it isn't torn. In my opinion, 10 clicks is really overdoing it. Once it clicks 3-4 times, it's tight.
Thanks for the top-notch info.!

I'll take a look myself after I get the car back from the dealership -- they have the car, they had the car when we had the conversation I mentioned, the car is at the dealership now. They called me to tell me the two codes from CELs and I let them know the circumstances under which the evap code happened because I wanted them to consider more than just let it go as "owner failed to tighten gas cap," which is to say it is possible I made a mistake on one occasion, but I am really anal about tightening that cap and I don't know any better, but I'd have thought 200 miles into a tank of gas was an unusual time for that CEL to show (I'd expect it to happen shortly after filling up).

I have no easy way of lifting the car at home, is the evap canister under the rear bumper easy to find and see?

As for 10 being overdoing it, yes, I can see your point, but it appears not to tighten after four or five, could I be harming the gas cap by going 10. I just have always wanted to reduce the chance of throwing an evap CEL. <g>

Again, thanks for the expertise.

Cheers,

Sean
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Old 01-30-2006, 11:45 AM   #7
solbey11
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My mom has an 02 WRX sedan and I'm pretty sure the canister is on the passanger side right in front of the rear bumper. And it's the same place on my 96 Legacy.

I don't think you can actually hurt the fuel cap by tightening it 10 times, because it's limiting how tight you can get it by clicking.

I read you can plug the green diagnositic connector under the dash and listen to the drain valve and purge control solenoid valve. They should both start cycling on and off whenever you have the key on/engine off. If they are turning on and off, it means they are functioning properly. It's worth a shot if you can't find any leaks in the evap lines.
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Old 01-30-2006, 11:49 AM   #8
SeaRex
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Great info.!! Thanks.
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Old 01-30-2006, 11:52 AM   #9
solbey11
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Oh, and I see that they have your car now. At first I thought you just called them looking for an over the phone diagnosis. I completely understand now.

No problem on the information buddy. I'm an unemployed tech right now so I try to help when I can.

This is an excerpt from a write-up I did on RS25.com. Even though your car is a WRX, the evap systems are pretty much the same between models. It explains how the evap system actually works. And if you have an understanding on how it works, it may be easier to diagnose yourself.

Quote:
Canister Purge Control explained…

Your evaporative emissions control system was created to control pressures within your fuel tank. Whenever air pressure builds within your fuel tank it is very unsafe. Before evap systems were created, the excess pressure was vented into the atmosphere. Within that excess pressure are fuel vapors. In order to control the loss of those vapors, the vent valve is attached to a Canister filled with activated charcoal. When pressure is released into the canister, the activated charcoal will absorb the fuel vapors. Then when commanded by the ECM, the purified air will be released from the system by the Drain Valve. Once enough fuel vapors are contained within the Canister, the ECM will activate the Purge Control Solenoid to send those vapors in through the intake manifold to be burned off within the engine.
This is the write-up if you are interested...http://www.rs25.com/forums/showthread.php?t=40632

I hope this helps you out a little better.
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Old 01-30-2006, 11:55 AM   #10
SeaRex
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No worries, I wasn't exactly clear about the fact that the dealership had the car and you gave me several things to follow up with.

I'll checkout your write-up.

Cheers,

Sean
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Old 01-30-2006, 12:13 PM   #11
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At 120K it is very likely that there are some deteriorated hoses, clamps etc. Sometimes the canister and associated hardware can be damaged from road debris impacts since that stuff is in a vulnerable spot under the car. A bad solenoid or valve would probably set its own code but not necessarily, depending on the nature of the failure. There are also some hoses and a valve in the engine compartment that can break or come loose.
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Old 01-30-2006, 12:31 PM   #12
SeaRex
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Thanks.

In a state like Connecticut, with some poor roads, road salt, etc., I can imagine it might happen that a hose gets damaged or something. I hope the dealership will consider what I offered and check it out while they have it on the list, cos they know better than I what to look for and have a more comfortable time (versus lying on a dirt, icy, cold driveway) doing so.

Cheers,

Sean
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Old 01-31-2006, 12:08 AM   #13
kdogae86
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personally i would have erased the code to see if it would come back. sometimes the planets dont align properly and all the sensors dont communicate nicely and the little light will pop on. if u can find some sort of smoke machine than u can force it into the system so that if there is a leak than the smoke will escape.
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Old 01-31-2006, 12:50 PM   #14
SeaRex
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The code has been erased. Maybe it is a planet thing. Will see ....
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Old 02-01-2006, 09:46 AM   #15
SeaRex
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Been through a tank. No CEL. Maybe I was in error or maybe the planets did burp. Running smoothly as ever.

Cheers,

Sean
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Old 01-17-2008, 12:00 AM   #16
ejicon
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this is great info... SeaREX: did that code ever come back?
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Old 05-12-2012, 09:07 PM   #17
SpastikMooss
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I know this is a super old thread, but I'm having issues with my car overheating at highway speeds only after this cel popped up. Could the two be related?
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