Just replaced the shut off valve this past weekend. Like most others the original was so rusted on I had to replace the canister as well. I also vacuum checked both hoses coming off the canister and they checked out fine. After driving the car to work and back, p1456 code came on. I checked the gas cap (brand new OEM Honda) and got no hissing noise. Great. The O-ring that comes with the canister, that is for the vent shut off valve, right? P1456 should be a leak on the fuel tank side, which I haven't had a problem with yet. I feel like I must have missed something installing it but all the hoses are in the correct location and all electrical connectors firmly pressed in. There isn't an o-ring that goes on that larger click-in-place hose that goes to the fuel tank is there?

JimBlake - as explained in the OP I originally tried to go through the procedure but got stuck at a point and could not go anywhere. So I got sick of it and started throwing parts at it, yes I know that's not the right way and I would not recommend it to anyone else either, I'm just getting sick of diagnosing this thing.

 

So, after all that rambling....what can cause the gas vac leak for p1456 code from replacing the canister and vent shut valve? I used the o-ring on the shut valve, and everything is plugged in correctly the same way it was before. The only thing coming from the gas side is that click-in connector to the canister, right?

Yes, I've clicked the gas cap 3+ times and have always had a hiss prior to this. I just went and re-checked and it's the same thing.

 

For the fuel cap, techs sometimes cleans the gas cap seal and then add a little grease to help the seal.

With the ignition switch OFF, you can reset the ECM/PCM by removing the No. 13 (7.5A) Clock BackUp from the passenger side fuse box for 10 seconds.

P1456 is a two-trip code. Once cleared from the PCM, it cannot be reproduced in one drive cycle. Additional test drives may be required to reproduce all driving and ambient conditions required to set this code.

See attached pic. for some info.

 

The gas cap is a brand spanking new Honda OEM unit. I have always heard a hiss while cracking it open. I've never had P1456 before.

After the vapor canister and shut off valve install I have P1456 code and an obvious leak between the gas cap to the vapor canister. I have already triple checked the seal on the gas cap and started it up/checked for vacuum. After the install, I get no hiss, nothing. Prior to that it was nice and tight.

What am I missing?

 

The only odd thing I noticed during the install was that the two way valve appeared to be leaking gasoline while I had it tipped over and trying to wrestle the shut valve off. Could the gasoline have damaged the two way valve and now I'm not getting the correct vacuum seal to the tank?

 

Now I'm wondering if the charcoal in the EVAP canister is saturated? When I was messing with mine, there wasn't any liquid in there. Do you normally fill it up to the brim? I usually don't but I'm not always real careful either.

For that matter; redbull do you think liquid in the EVAP canister might cause P1457? In which case maybe you can simply dry it out?

 

If the canister was saturated with fuel, I would think there would be some different DTC code(s) such a P0440.

Both P1457 and P1456 are usually are indicated when the ECM/PCM tests the EVAP system integrity by applying a vacuum signal and monitoring the ability of the system to hold vacuum. If the system doesn’t hold vacuum for a specified period of time during the integrity check, it indicates leak(s) in the EVAP system.

There is a possibility it is related to the EVAP Bypass Solenoid Valve set. From reading his posts, it doesn’t indicate he replaced that. It sounds like he replaced the canister vent shut valve and canister. For P1457, on the 6th gen Accords, it is a leak at the canister side which may be due to various causes; however, the canister vent shut valve and/or the EVAP Bypass Solenoid Valve are usual suspects due to water possibly getting in and causing corrosion and damage. Sometimes one or both of those valves may be damaged by corrosion.

For P1456, it is a leak on the gas tank side, which can be due to the gas cap, EVAP Bypass Solenoid and 2-way Valve (generally the EVAP Bypass Solenoid and the 2-way valve are replaced together as a set),or some other cause. If he didn’t replace the EVAP Bypass Solenoid Valve set and it is faulty, that can possibly be the cause for the previous P1457 code and now the current P1456 code. If the 2-way valve leaks, it can allow the fuel tank pressure to decrease, as it goes into the canister and the ECM/PCM can set the DTC P1456.

Although the leak may be caused by something else; I would be looking at the EVAP Bypass Solenoid Valve as a possible cause.

 

I don't overfill the tank. Plus, I just replaced the vapor canister.

 

In the OP I said I replaced the bypass solenoid valve (two way solenoid valve) but not the two-way valve.


So far I've replaced -
1)Bypass solenoid valve - still p1457
2,3)Canister vent shut valve AND vapor canister - now p1456 and no hiss when opening gas cap


I've just now double and triple checked all of my connections under the car and I can't find a thing. Really the only thing left replacing under the car is the two-way valve itself.

 

I replaced the two-way-valve with a new OEM unit and reset the code – P1456 came back

I then took off my new OEM vapor canister and shut valve and inspected the o-ring to make sure it was seated. I also checked for proper vacuum and it was OK. Put it back together – P1456 came back

After doing another inspection I noticed a cracked vacuum line at the plastic nipple under the gas tank behind the drivers side rear tire that goes up to the charcoal filter. Aha! That’s gotta be it! Replaced that, reset the code, and guess what – P1456 came back.

I am seriously at my wit’s end with this car and don’t know what else to do besides take it to a dealer or mechanic who will probably charge me $450 in diagnostics and then replace some mundane piece of vacuum hose. It’s either that or park it in a field and light it on fire. It’s like I’ve literally worked backwards on this car and went from 1457 to 1456 and it’s frustrating as hell.

So far I’ve replaced the Two way valve solenoid, two way valve, vapor canister, canister shut valve, gas cap, and now vacuum hose.