I'm trying to find the name of the circled part in this picture. I think it is a One-Way Vacuum Check Valve. Maybe this? It has two foam doughnuts/"bumpers" on each side, black and light gray. It joins two black tubes. Mine is hissing. It has a crack on the white side. The check engine light came on and is now off, but only because I disconnected the battery when trying to make sure this part is the cause of the hiss. I'm sure the light is destined to come on again.

The car runs fine, but I'd like to get any input one what harm this is doing to determine urgency in getting this fixed.

Oh, it's a 2007 Mazda 3 5-door. First post, first problem with the car.

 

It looks like a purge valve for the evap system.

 

Thanks. Found a closer picture and have circled the part with the crack. From what I can tell the all black piece on the right is the purge solenoid valve. Does the black & white valve have a specific name (other than what I'm assuming is "vacuum check valve") or is it essentially part of an assembly.

Apologies for all the newbie questions. I'm trying to get a bit more educated before I walk into the dealership. If I go in and suggest, "The vacuum check valve next to the purge solenoid valve has developed a crack." is that going to make sense?

The car is under warranty, so I got that going for me. I am assuming they'll replace the cracked piece only, which is fine with me, as long as it cures the problem.

 

The part you mentioned does look like a vacuum check valve, it looks like it comes with the tube and purge valve assembly.

 

Thanks again. It's all coming clearer.