Hello, hope the new year finds you all well.


First off I am FNG to the site, aircraft mech for 14 years now, and work on my cars to save money.


I read a lot of forum threads on p1457 and typically reading threads I never have a need to post.


Step 1
I have pulled the EVAP canister with vent valve attached jump the vent valve with 12v and vent valve works.
Step 2
I reinstalled the evap can etc and checked wiring for 12 v at pin a4 on back side if pcm/ecm and I have good 12v. So I know the pcm/ecm is not providing the require ground for vent valve


Here is where I am stumped, the Chilton manual leads me to believe that by turning on the ignition that the PCM/ECM will provide ground to pin A4 in turn closing the vent valve. If that is the case replacing the ECM/PCM seems to be fix. However I don't know the logic inside the PCM is it simply ignition ON vent valve ON or is there other condition that must be met.
Not sure if auto world publish logic diagram ( And, OR , AND/OR gates)


Any help would be great and if I cant simply see the trees because of the forest feel free to slap me in the back of the head.
Thanks

 

Refer to the links in post #4 of this thread:
https://www.hondaaccordforum.com/for...e-p1457-57080/

 

I did see those threads. I will go down the road of ops checking all those valves but would like to rule out pcm/ecm first. I did talk to dealer and the did work on it in the past and replace the bypass valve. It may not be till next week till I get back to accord, headed out to garage to replace pan gasket on civic.

 

In regards to the above, when the ignition is ON or START, power (+) is supplied to EVAP Canister Vent Shut Valve; however, turning on the ignition doesn't automatically supply the ground (-). The PCM controls the valve and supplies the ground (-) under certain conditions.

If ground and power were always supplied to the vent shut valve, the valve would remain closed all the time when the ignition is ON; additionally, it wouldn't even need to be connected to the PCM.

 

Testing should be done instead of just replacing a part. We don't normally advocate just throwing parts at a problem on this forum. Usually, it is more likely due to a leak or a faulty canister side related component than the PCM being the cause of P1457.

 

redbull thanks,
It wasn't making sense so I went back to manual and found that the system is control engine temp and few others condition,


trust me I wasn't going to shotgun parts at it.


and now that I have my head out, I am going to check rest of the valves, later


Feel free to delete this thread if you feel it may confuse anyone else