Quote Originally Posted by BillBoost37 View Post
I'm a bit ruffled by your guessing at how these items work when I specifically directed you to exactly how they work, how the codes are set and what must happen for that to occur.

Not trying to ruffle feathers....just trying to understand. I went to the link you provided as soon as I saw your post.

>>I just reread the info on the two codes. Pretty interesting stuff that unfortunatly the way it's there, can't be copied. Wish I could, because I'd post it up showing how 440 tries to pull a vacuum on the tank to tell if there's vacuum (aka force to collapse, IDK?) and uses the tank pressure sensor (452) to show if it sees a high reading. High means vacuum, low means that there isn't vacuum in the tank...low means it sees pressure.

My follow-up question was how these 2 play together. In other words, if the system thinks the sensor is bad, does it really still think there's a leak and report both? Which one is run 1st....I don't know and it's not clear from the link. If I were in charge of setting things up, I would test the pressure sensor 1st to make sure I get a believable reading....if not set a (452) and stop there because any following test doesn't make sense. But that obviously is not how it is run or both codes wouldn't set. Since I have a (452) do I just ignore the (440) or is there something else to be wary of when I get both codes? Is there some other component that can fail and cause both codes to set? Those are the types of questions I have even after reading the DTC links.

>>If your pcm is telling you it thinks you have a vaccum leak in the evap system because it's not generating vacuum according to the tank pressure sensor, which is setting a code to say there's a problem. And let's add that your tank is collapsing... because the evap system is continually trying to pull a vacuum on it. I'm thinking these two codes give you probable cause to believe that the pressure sensor isn't reporting the vacuum that is potentially collapsing the tank.

Like I said though..I'm sure you've already put this together yourself and are probably looking for someone else to confirm for you.
No, I don't have it all figured out. That's why I have posted my thoughts/questions (as silly as they may be) to allow all the people who know a lot more about this stuff than me to correct my thinking....so I can learn.

The assumption of a bad pressure sensor reading makes a lot of sense, but even after reading the DTC links you posted, it's not clear that that's my only problem. If I am reading correctly, purge valve not opening can also cause that code to set. I just want to make sure that I don't install a new tank only to have it collapse again, so I am trying to cover all possibilities. And I don't even know that the collapsed tank is related to the DTC's...that's why I put my assumptions down for all to critique. I would like nothing more than to be reasonably sure I'm not going to collapse a second tank. I don't have ready access to shop/equipment, and have limited time to work on the vehicle. I am trying to account for all possibilities at one time.....I don't want to pull a tank and replace...only to pull it again to replace an EVAP canister or purge valve or etc......

I fully expected someone to reply to my post correcting my thoughts and assumptions on the force on the tank. That would be more than welcome if I've made mistakes. But I am surprised to get a 'ruffled' response to honest questions and an honest attempt to learn.