Thread: DTC Codes P0440 and P0452

Previously asked a question about what could cause fuel tank to collapse, and if faulty evap system could collapse the tank.

Finally got access to scanner and was able to read 2 codes:

P0440 and P0452, both related to the evap system.

P0440 seems to be a generic evap system code, while P0452 references
low pressure sensor input.

What I know: Fuel tank is collapsed, without any indication it has been physically hit or dinged from below. Fuel level sending unit is stuck at 1/4 tank. It is passing a solid believable reading to the PCM (not open or floating around), and I suspect it has somehow wedged against something on the collapsed tank and stuck. It did read correctly after install, until tank got low for the 1st time.

Here's my thinking, please provide any insights or information that might be helpful.

Bought the car approximately 6 months ago, and fuel level sender did not
work from time of purchase. Only code at time of purchase was 1 that indicated "leak or missing gas cap" (don't remember the #. I suspect the person I purchased from knew he had an evap problem, erased the codes, and avoided completely tightening the gas cap to prevent tank collapse. Soon after buying car, my son reported hearing noise from the rear of the car, which in hindsight was likely the metal tank "oil canning" as it collapsed. Cannot be sure when the codes were set, since "check engine" light is either burnt out or disconnected.

I suspect fuel tank was collapsed when I first replaced fuel pump/sender unit, but not absolutely sure, due to unit trying to "kick" to 1 side during install makes me think the tank was collapsed and slanted.

Do I need to erase the codes, or will they update and go away if the old sending unit pressure sensor was bad and I now have new (presumably good) sensor that came with new pump unit? I'm wondering if a plugged purge solenoid caused vacuum to be pulled, and also the "low pressure sensor input". Or is it more likely that a bad pressure sensor (or wiring) caused a too hard a vacuum to be pulled on the tank?

Either way, don't mind replacing the tank, but want to make sure to determine root cause so I don't just collapse a 2nd tank.

Any insight appreciated!!

Just remembered that the fuel tank pressure sensor is a negative slope sensor, so low pressure = high output and vice versa. So pulling a hard vacuum would not cause pressure sensor low voltage output.

Is it possible that a low voltage (system would think high pressure) would cause the system to keep pulling vacuum and therefore collapse fuel tank?

Sorry if seems like a silly question....but here goes:

How can the system determine that there is a "large evap system leak" (P0440) if the pressure sensor output voltage is low (P0452)?

I'm assuming a P0452 code would be set if the pressure sensor voltage was unbelievably (out of range) low, like below 0 - 0.5 volts, indicating the pressure sensor (or harness) has a problem.

But if the pressure sensor or harness has a problem, the sensor voltage could not be used to determine there is a leak in the system? Right?????

Or does the combination of codes mean the system is not capable of pulling a vacuum (because the pressure sensor output stays low), therefore, assume there is a leak (but the pressure sensor output is believable, just high in range, ie: low voltage).


I've read a lot of different discussions all over the internet concerning whether an engine can pull enough vac to collapse a tank. I must admit I really don't have a feel for whether it is possible or not. How much vacuum will the GTP engine generate? If I knew that, I could translate to PSI of force and do a "sensibility check" on the possibility.....

Ok a quick followup/sanity check on the collapsed tank:

From other posts on this forum, I've read the GTP pulls 18-20 inHG vacuum (at idle). Don't know if this is correct or not, but will assume this is the ballpark vacuum.

Assuming 20 inHg vacuum means engine pulls this far below atmosphere, which I believe is correct when speaking of vacuum gauges (instead of absolute pressure), then the engine is pulling down about 2/3 of an atmosphere (1 atm. = approx. 30 inHg = approx. 14.7 PSI) or 10 PSI (my head can think in PSI, not inHg).

The fuel tank in the GTP is 33.25" x 27.75" x 11.75". The top of the tank is 2 "levels" which would make it tough for my mind to understand exactly how the pressure would be applied, but the bottom of the tank is relatively flat (yes, there are some ribs and bosses).... if you consider it as 1 surface, it has an area of roughly 890 square inches.

Applying 10 PSI across 890 sq. inches and the force being applied to the tank would be 8900 lbs. I could believe that would be enough force to collapse the tank. Even if my data is wrong and the engine only pulls half the vacuum, that would still result in nearly 4500 lbs. of force. Off by a factor of 4 would still give approx. 2200 lbs.

It would seem believable to me that any of these forces could feasibly collapse a tank......

I might add that my son reported hearing the "clang" as he pulled into the driveway....car is warm, evap system could be running, and engine at idle, pulling the most vacuum.

Are my numbers here correct? Please correct any errors in my numbers or thinking.

Hey longshot,

Bill has helped me in the past and I have followed his post on other peoples problems which has helped, he knows his stuff and you can't go wrong following him, if Bill Boost, Drunkie, Brandon or Swiggles is working without you are getting some good help if you don't understand something ask them they will explain it. I got a similar Problem with a 441 code Bills helping me with this currently.

Logan541

Originally Posted by BillBoost37

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.