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I started another thread last week asking about the main relay because I was chasing a fuel issue. The check engine light was on and I was getting a p1456 code. So I ordered about $200 in parts yesterday morning to hopefully resolve this, but by the afternoon the check engine light mysteriously went off. So I checked my OBD2 scanner and now it is showing only a P0420 code but no check engine light illuminated. So I assume I need to change O2 sensors and/or catalytic converter. I find it strange that the P1456 code went away on its own and now I'm getting a P0420 but the check engine light is not on. Has anyone experienced anything like this before?

 
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I'd just wait til it sets a mature code with the CEL on, then erase it, and then drive it to see if it will reset the same code, repeat at least couple more times before taking action.


Also could be a flaky code reader giving you wrong codes. That's a real problem sometimes.

 
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Thanks for the reply. The check engine light came back on this morning along with the P1456 code. I cleared the codes, will replace the fuel system components I ordered, and see what happens next. I just need to make sure I can pass emissions inspection by August.

 
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What parts do you plan on tossing at the car?
Also, what year is the car?

 
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Vapor canister purge valve, vent valve, and fuel pressure sensor. I also ordered a new gas cap. It's a 2001 EX.

 
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Purge and vent (CVS) are probably the most common issues I see. There's a tsb on the purge valve too.



If you're in the rust belt the CVS screws may be stuck in the canister and put up a fight.

 
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I replaced these parts and erased the code a few days ago. L was feeling good that the CEL was not returning but it came back again this morning. No P0420 code but P1456 and 1456P are back.☹

 
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Did you search the forum for P1456?
Code is for a leak in the tank side of the system.



You've still got a couple other valves involved in the system that you didn't replace.....though it may even have a real leak causing the tank to not seal well enough to hold a vacuum. Do you ever smell fuel like in the garage?

Rodent gnawed a hose somewhere above the tank?

Smoke check?

 
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ezone, thank you for your continued help.
Yes, I’ve done a search for the 1456 code on this forum and on the internet in general. I’ve never noticed a fuel smell, but I don’t typically park this car in the garage either.

I’ve been chasing trouble codes for a while now. I was getting one for random misfire that has since been resolved before this one started. I took it to a shop that specializes in Honda several months ago and they said they detected a small leak in the fuel tank. I was told a valve on the fuel tank needed to be replaced at a cost of $2k. I assume he meant the fuel tank vent valve but wasn’t convinced of this assessment.