That's good. I've never had an issue returning anything back to Rock Auto. It was making me made reading about it.

Hope the issue is resolved?

 

This car has been through two tanks of gas with no further indication of this problem.

 

I have 1998 Accord 4 cyl. When I got this car, it through a P1496. I replaced #26 and #27 on your first diagram. Also replaced an O-ring that is between those two items along with hoses that connect to #26 and 27.
Been 6 years now and so far so good.

As for you last entry.. right, you never want to "top off" your car. I had the bad habit of wanting to round it off to a flat $.. Like $26.00- not a good idea, unless its like within 25 cents.

 

Or, you're on a road trip, and you're going to burn that "top off" off.

 

My friend has a 1999 2.3 Liter Accord. His recent experiences mirror Gordon2's very closely. Here's the timeline:

March 2020:
Accord was throwing a P1456 code. A shop replaced the Evap Two Way Valve. The P1456 code went away. But within a day or so, the engine was throwing a P1457 code. This is just like Gordon2's experience. Also my friend's Accord smelled of gasoline fumes after driving.

Fast forward to July 2021:
My friend and I studied the net on how to proceed. We had not yet seen Gordon2's thread. We tested several parts of the Evap system. Nothing seemed to be broken. Still we decided on a kind of shotgun approach. My friend and I went to a salvage yard and bought a bucket of 1998-2002 Evap system parts (charcoal canister, Evap bypass solenoid valve, Evap two way valve, Evap vent shut solenoid valve, and fuel tank pressure sensor); cleaned them all; and tested the two solenoid valves. The salvage yard Evap Bypass Solenoid Valve failed the electrical test (applied 12 volts; no click; no change in flow pattern for the solenoid valve's two ports). My friend and I unfastened the salvage yard Evap Bypass Solenoid Valve from the salvage yard Evap Two Way valve. My eagle-eyed friend noted the two O-rings. Then my friend and I unfastened his Accord's Evap bypass solenoid valve from his Accord's Two Way valve. We found no O-rings. My friend and I believe the shop in 2020 did not install any O-rings.

My friend and I installed the two O-rings we had handy from the salvage yard parts. Like Gordon2 describes above, I am a little concerned the mating surfaces for the Two Way Valve and Evap Bypass Solenoid Valve are a bit ****-eyed, due to the O-rings. Still, we plugged the ports of the assembly; applied soapy water; pressurized the assembly; and saw no leaks. After re-installing all (but now, with O-rings), my friend and I test drove the Accord for a good half hour or so. So far so good.

Edit: See JimBlake's attachment below for how to set the evap leak monitor "readiness code." Thank you JimBlake.

For do-it-yourselfers, replacing the charcoal canister and the several parts in and around the canister (two solenoid valves; two-way valve; pressure sensor) is not difficult. My friend and I did jack up the rear left of his Accord; placed two jack stands on the inboard end of two of the rear left wheel's control arms; then lowered the Accord onto the jackstands. We put a huge wood block under what looked like a hefty structural member a few feet forward of the Accord's charcoal canister, as a back-up. This greatly facilitated access to the canister and other parts.

Main steps for replacing the Evap Two Way Valve O-rings:
-- Chock the front wheels. Loosen rear left wheel lugnuts. Jack up rear left of the Accord.
-- Put inboard ends of two of the hefty rear left control arms on jack stands.
-- Remove rear left wheel.
-- At the canister, disconnect certain hoses and two or three electrical connectors.
-- Drop canister (one 12 mm bolt at canister's otbd side; be mindful of the clip on the canister's inboard side).
-- Remove the two-piece plastic box around the Evap Two Way Valve and Evap Bypass Solenoid Valve.
-- Remove two phillips screws holding bracket (screw heads facing aft). Then the Two Way Valve and Bypass Solenoid Valve are free?

Here's a photo of the Dorman Two Way Valve and O-rings:



The Honda p/n for the 2.3L Accord's Evap Two Way Valve is 17371-S84-A01.
The equivalent Dorman p/n is 5981-01427860.
Photos on the net for both these part numbers indicate the O-rings come with the Two Way valve.

Evap Two Way Valve O-ring part numbers:
91392-S02-000, replaces 91392-SV4-000
91393-S02-000, replaces 91393-SV4-000

I measured two used O-rings and found:
Larger O-ring seems to be size A012, 9.25mm ID x 1.78mm thickness.
Smaller O-ring seems to be size A010, 6.07mm ID x 1.78 mm thickness.

I suspect the O-rings are not viton, though viton may be desirable

Consider replacing the Evap Canister Vent Shut Valve O-ring as well, part number:
91391-S84-A00

Update, July 27, 2021:
My friend has taken his Accord on the highway a few times now. The Evap readiness code would not set the first couple times. Then he took another drive and checked: Success! The Evap readiness code is now set. The Accord still has a faint fuel smell near the rear left tire. My friend and I may replace the O-rings with new ones and/or replace the vent shut valve O-ring.

Update: September 5, 2021:
No CEL. All remains fine.

 

I'm not sure why I didn't catch this during the original thread, but here's how to set the "readiness code" for the 1998-2002 EVAP system. It isn't as simple as 2 drive cycles...