Can someone please explain the difference to me? I had a couple of P0449/446 codes on early morning or rainy startups. I ordered both parts and just installed the Solenoid. Old one had a bunch of fine dust in it. Haven't had a chilly morning yet to try a cold start, but it seems to be starting and idling better. Just curious if I should still replace the Purge Valve while I have it and am somewhat motivated to do it.

 

You got it, I replaced my vent valve due to stuck closed. My purge valve is still oem. No need to replace if it aint broke.
The Vent Solenoid is a normally open valve that is commanded closed to seal the EVAP system and stop air flow into the charcoal canister. The Purge Solenoid is normally closed but is opened by the PCM to allow manifold vacuum in the EVAP system — thus drawing fuel vapours from the EVAP system.

 

Thanks Hummerz! Do you know what signs in performance or code would point to one or the other?

 

Malfunction Outcome
Malfunction of the canister vent valve, it means it is either stuck closed or stuck open.If it is stuck closed, the fuel system venting will be blocked and there will be pressure or vacuum generation inside the tank which would affect in-tank fuel pump operation and the gas tank overflows when filling. This will cause engine hesitation, vehicle starting problems, difficulty in filling the fuel tank, loud noise coming from the fuel tank or fuel cap, engine emission failure, and will get diagnostic error codes in case of EVAP venting integrity test.

 

Well I'll be darned. That would explain why the pump clicked off yesterday then vomited about 2 cups of gas on the side of my Hummer. Thanks Hummerz, very helpful.

 

Has anyone experienced issues with the Vapor Canister Vent Solenoid that DOES NOT involve an issue with filling the tank or accompanying DTC? I'm having trouble figuring out how/if this part could be impacting my longstanding rough start issue. Seems unlikely, considering I've been experiencing the same issue for ~8 years and I've never received a code. If the H3 occasionally starts up and then very quickly gets bogged down and loses nearly all power (sometimes stalls completely but not every time), could this be attributed to an issue with the opening/closing of the vent solenoid? I have replaced the purge valve, camshaft/crankshaft PS, fuel injectors, MAF, and throttle body is clean. Also replaced the gas cap with GM OEM H3 locking gas cap. Never received a code or idle/stall issue other than at startup.

 

check for intake plenum gasket leaks. at minimum try retorqueing them.