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I am checking the civic service guide and it never references p1457 being the fuel cap. p1456 is the fuel cap. I understand that 1457 is the canister area. I replaced the EVAP canister vent shut valve and the code returned after clearing it. My fuel cap seems clean and the o-ring looks good. I even get a vacuum hiss sound when I unscrew it. I have three clicks when tightening the fuel cap. Also I live in California and the EVAP region appears to look in very good shape. I see many people saying to replace the fuel cap with the p1457 but I am wondering how that could cause a canister area code. The service manual contains many electrical steps to diagnosis the 1457 which I am not equipped to do. I want to avoid a shop at all costs.

Should I go for the canister replacement now or just shell out the 15 for a fuel cap?

Would the fuel cap have a leak if I have a hiss when I open?

 
Rep Power: 223

It's not the fuel cap. Here's a good pic trying to show where in the system each fault would point to (stolen from the Youtube video link below). This is based on an Accord but the system is similar in design. A popular cause of the fault is the canister shut valve (CSV), usually on rust belt Civics though.

 
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Thanks but unfortunately I replaced that already and cleared the code like I mentioned above and the issue remains. I called it the two-way vent though.

 
Rep Power: 223

Did it look like this? Because it sounds like you replaced the 2-way bypass solenoid valve.

 
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Yes that is the part. Sorry i'm getting confused by the names. Changed that and went to recheck this afternoon; all the hoses around the canister and everything else feels and looks sound. I used a Dorman 911-762 or canister vent solenoid but it had good reviews. I might shell out some extra money for a genuine part but I doubt it will matter.

 
Rep Power: 98

People here may tell you that ONLY OEM parts will fix your problem. That may be true as I've seen some videos where new aftermarket EVAP parts cause the same problem or a completely different one. But I agree with you that replacing the Dorman part with a Honda one probably won't fix the issue.

Replace the canister. When I had a P1457 code, I did what you did and just replaced the valve (I call it the canister vent shut valve, not the bypass valve). This did not work. I then replaced the canister and erased the code. Problem solved. It's been almost a year with no EVAP codes.

BTW - I used Standard Motor Products brand parts. I also bought brand new screws that hold the CVS valve to the canister rather than trying to re-use the old screws.
Also, I tried replacing the gas cap also. That did nothing.

 
Rep Power: 223

In this case, I would tend to agree with that.

I would not recommend just replacing parts without troubleshooting first. If you have a hand vacuum pump/gauge there is some easy testing you can do. Another possibility is the EVAP purge valve up on the intake manifold. The last P1457 I troubleshot I found this valve was chocked full of mud. Once cleaned I found the valve was stuck open causing a leak.

 
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I will keep everyone updated on how it goes. I only have access to a jack on the weekends so I can only do repairs then. Plus there is the approximate 3 day drive cycle until I figure out if the replacement really worked. I really want to do the correct troubleshooting procedure but I am a novice and its tempting to swap a part when it could save you hundreds at the mechanic. Kind of like gambling.

 
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You were correct! I replaced the canister yesterday and so far for the last 60 miles the CEL has remained off. It seemed to turn back on after 50 miles when I reset it before. Interestingly enough the old canister felt heavier (must be full of stuff) and the new canister sounds like beads are rolling around inside while you tilt it while the old one does not make any noise.

Fuel cap never made a difference and I thought it would not but you get so much information on the net that sometimes you feel like maybeeee but no.

 
Rep Power: 221

Old canister is completely saturated with gas, new canister will be dry

 
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It is with great disappointment..the check engine light is back with p1457. The strange thing is that after I replaced the canister the light did not return until 120 miles later. Whenever I cleared the code previously the CEL always returned at 50miles. Maybe its coincidence but I had partially fueled by tank the morning of. I did seal the fuel filler cap through pretty well and that is another code entirely. I guess next is the smoke test. Any suggestions as to what else it could be? I checked the hoses with my naked eye but I can not be certain a pin sized hole exists.

 
Rep Power: 223

I wasn't going to say anything when you said it was fixed but replacing the canister didn't make sense to me. The fault is saying the system is leaking, unless the canister had a crack/hole it shouldn't have fixed the code. The code coming active after filling up is pretty normal. One of the first steps for the troubleshooting I've seen says add a gallon of fresh fuel. Do you have a vacuum gauge/pump like this?

 
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I do not have a pump or a smoke machine. I think I will just take it to a shop. I cannot work on the car unless its Saturday and I am not that skilled a mechanic. Thanks for your advice though. Strange enough through that replacing the canister seemed to delay the return of the code?

 
Rep Power: 223

Probably just a coincidence I would guess. If you change your mind and want to troubleshoot let us know. Using a vacuum pump and a multimeter you can get pretty far.

 
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One last thing I just noticed on an earlier reply of yours. The intake manifold purge valve; when I had a part replaced near the intake manifold the work was shotty and I wonder just wonder if that is the location of the issue. I am really trying to use your advice to not just blindly throw money at the car - and I do not think I will anymore without professional skilled diagnostic but the temptation just to look.. is well tempting. I am going to look at that region this afternoon. Is that something I can visually see without taking to many parts off? You see I live in an apartment and do not have space for a jack and we cannot work on cars in our complex.

 
Rep Power: 223

I can't remember what has to be removed to get to it, I think just the air box where the air filter is. The purge valve should have two hoses and one connector. One hose leads to the throttle body/intake manifold and the other goes to the firewall and eventually back to the canister.

One of the first troubleshooting steps is to check that valve. It is normally closed so if you get to it, take the hose off that leads to the canister then try to suck air through the valve. You should not be able to. This is easier and not as gross if using a vacuum pump/gauge. As I stated previously this was the cause of the last P1457 I looked at. The valve was stuck open meaning the evap system was leaking through it.

 
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Found the part. Its not difficult to get to I think it only requires me to remove the air cleaner element. The part is showing at this . I will let you know how it goes.

 
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I changed the Cannister Purge Valve this weekend. Air filter screws were difficult but other than that it was a fairly easy replacement. Drove for 100 miles and no code. Took it to get the car smogged today. Special thanks to BrotatoChip!