Which way does the vacuum check valve go?

twlaub · Post by **twlaub** » 25 Sep 2009, 08:57

This may seem silly but I'm trying to track down a P0440 code and have been for some time. My specific question is about the orientation of the black and white check valve in the vacuum line. This valve is between the engine and the front of the car. I replaced it some time ago but forgot to notice which way the old valve was before removing it (DOH!). I found a vacuum hose routing diagram for the T-5 that has a picture of the valve with b/w sides but I just want to be sure. Should the valve allow vacuum to suck through it or not? That is, should the vacuum pull from the engine be checked? It seems to me it should.

Background on the code: The P0440 code has been plaguing me for months. If I reset the code it may come back in a day or may take weeks but it always comes back. Apparent triggers: After a highway drive when slowing down, cold/cool mornings.

Post by **MadeInJapan** » 03 Oct 2009, 07:29

White means open- black, closed- always the white towards the intake manifold. Hope this helps.

twlaub · Post by **twlaub** » 03 Oct 2009, 18:04

Thanks for the reply. I have the white side hooked up to the air pump solenoid valve which then has a line going to the air pump check valve mounted on the side of the engine near the fire wall. I think that qualifies as intake.

When I turned the check valve around, after about 2 days I got P0410: Secondary air injection system malfunction.

When I have it installed correctly, as it is now, I'll get the code P0440: EVAP emission control system malfunction. It may take a week or more for this code to come up or it may show up in a day.

I guess I'll try to see if the solenoid valve is working (you have previously said I could put 12 volts to it and it should open.)

Any other advice you have about tracking down this frustrating P0440 code is appreciated.

Post by **MadeInJapan** » 04 Oct 2009, 07:29

Could be a small leak from the back of the gas tank to the charcoal canister (not uncommon), so check that line too- often the one that hooks into the canister is broken...if it's broken at the right place, you can cut the broken part and reattach it.

twlaub · Post by **twlaub** » 04 Oct 2009, 10:07

Thanks I check that too when I have a whole day to work on it. I did fix a crack in that line about a year ago by splicing it but it was right at the canister and easy to get to. Tracking that line all the way to the tank is kind of tough isn't it? I haven't tried, but how do you get to the line? Isn't it way up inside the frame or some enclosed channel?

Post by **MadeInJapan** » 04 Oct 2009, 11:41

Not sure- if you're talking about your '98 XC, you shouldn't be posting in this section but in the regular V70 forum for that year- it should be no different...but I don't think it' sup in the frame. While under the car, can you try to follow it back to the back? It's often at the gas entry point....usually not between (if not at the canister again) as I believe they are hard pipes between. Or it could be as simple as a bad gas cap.

volvomileage · Post by **volvomileage** » 04 Oct 2009, 12:23

welcome back MIJ glad to have you around again

i have just a small question as per the black and white check valve if i am not mistaken there are two of them, one on the air pump soleneoid on top of rad and an other one on the tubbing that goes to the air pump tubing close to the battery ..

for both of them the white side shall point to the vaccum tree/ nipple/manifold ?

thanks

Post by **MadeInJapan** » 04 Oct 2009, 14:48

That's my understanding- I went through this some time ago and that's the way I routed them and haven't had any issues.

twlaub · Post by **twlaub** » 04 Oct 2009, 17:44

Sorry for posting in the wrong forum. I guess I didn't look close enough at the title.

Since volvovmileage gave another description of how the check valve should point I realized that is not how I have it. I have mine lit the one shown in the vacuum hose routing diagram matthew1 posted here https://www.matthewsvolvosite.com/forums ... mit=Search. On that diagram it actually shows a white and black side of the check valve and the white side goes to the solenoid. The black side goes to the vacuum tree/nipple/manifold. This seems to be the opposite of what you guys are saying. I am so confused....

Post by **MadeInJapan** » 05 Oct 2009, 16:22

Well, after reading your post I went out and checked under my hood and you're absolutely right- I've been telling you the opposite all along- black towards the manifold...grrrr...I'm sorry.

Btw, I moved this thread to the correct section of the forum.