I've had an intermittent P1457 for a few months now. I followed the troubleshooting procedure in the manual through step 26. I had to stop at the Canister System Leak Test portion since I didn't have enough fittings to make all the needed connections. I didn't find any faults with valves but did notice that I couldn't pull more then 7 to 9 psi vacuum. It would hold at that number, but would not go any higher. I've looked over the plumbing and didn't see any splits etc. I cleared the CEL and it stayed off for about 2k miles and now it's back on. Does anyone have any advice?

 

Sadly the best place to diag the evap dtc would be the dealer ship or at least an indepented honda service shop that has the tools/software to give a complete inspection and diag. However that being said the most common failures for that dtc are a bypass solenoid, 2 way valve and canister vent shut valve. Good luck!