[justforus2005]

Sorry to be blunt, but your posts read like a drunk person rambling on and on...

The P0447 is a circuit fault. That is, the ECM has detected an open in the vent control valve circuit.

View attachment 57152

nissian usa done work
they can’t solve problem 45 days sitting
on they lot
vent valve replaced
fuel pump parts replaced
oem fuel cap replaced
battery replaced
none fix the problem
code comes week after computer reset
now I take it sence every thing replaced
and they should be no problem
you not train well enough to figger this out
there 3 pressure sensors one on fuel cap
it sets on side of it
now one 3 sencors bad
or the computer set valves for valve no longer right
so it running off what old value was useing
guss what not dealership in USA knows anything about how reprogram the compter
you can flash it
you no idea how recode it
now they clame they know for fack fuel pump was leaking
if so would not the computer set new levels on it
and would they not be copy to new unit
so is this a software problem or still a reAl leak
3000 paid out
not fix but dealership
now have one fack
when computer reset get gas cap lose
keep in mind I got bran new oem gas cap

one two things wrong here eather software wrong

note also motor coolet sencor was -47 deg
tec clame was batteriy problem

or is this key prob that coolet sencor might be problem

 

[jbarnett250]

@I need coffee, do you think this thing is actually detecting an electrical short or open? I assumed the system was comparing the expected pressure versus the measured pressure in order to determine if the vent is working as expected or not. I've never read anything (or found anything to read) about how Nissan's evap test is conducted. The Toyota evap test is well documented and all the judgements that I recall are made based on pressure readings. Like if the vent solenoid is normally open then they'd expect little vacuum to develop when the purge valve is energized. So if vacuum is present when purge is open and vent is open, they'd conclude the vent circuit is shorted. And they'd expect vacuum to develop if the vent valve were closed so if no vacuum is measured, then they conclude the vent circuit is open. I wouldn't think they're actually measuring current flow and judging the electrical circuit open or shorted. Then once enough vacuum pressure is present, they close the purge valve and see if the system holds the vacuum for the set amount of time and either declare a large leak or a small leak or a pass result if the pressure drops fast/slow/holds. Is there a theory of operation for the Nissan evap tests somewhere in the manual?

@justforus2005, still don't know what code you're getting for sure...

 

[I need coffee]

@I need coffee, do you think this thing is actually detecting an electrical short or open?

That's the detecting condition--ECM receiving improper voltate signal through the vent valve.

Is there a theory of operation for the Nissan evap tests somewhere in the manual?

Search the service manual for "SRT" (System Readiness Tests) which is Nissan's term for the emissions readiness monitors and you can see a chart that shows approximately when the EVAP tests are run and under what conditions. Basically, you want to be driving the car shortly after engine warm-up in a place where you can cruise for a while going 50-60 mph. There's no good description of the actual tests that are run, but from what I can tell by watching fuel tank pressure on live data, it seems to be a relatively common set of tests. I haven't looked at it in quite a while, but from what I remember it would purge with vent open (test if adequate vacuum can be achieved during normal purge) and then close the purge valve and leave the vent open (test for drop in fuel tank pressure indicating a faulty purge valve that can't fully close), and then close the vent valve and open the purge valve to draw a big vacuum and then close the purge valve to watch the rate of vacuum decay (with both valves closed), and then it would open the vent valve (probably also watching how quickly vacuum is released to check for inadequate vent function).

BTW, I'm not sure what the other poster was talking about with the tests running with engine off. There is such a thing, but Nissan doesn't use it in the 1st or 2nd generation Murano although maybe they did introduce it at some point in the 3rd generation? It's called Engine-Off Natural Vacuum (EONV). Some manufacturers moved to EONV systems to search for really tiny leaks. How it works--basically, when warm fluids cool in a sealed system a natural vacuum develops. Well, manufacturers have used the fact that the fuel pump warms the surrounding fuel to use this effect for leak detection. When the engine is shut off in an EONV system, the purge and vent valves are closed and the ECM will literally wake up in the middle of the night to check fuel tank pressure. Based on how long the engine was off, the ECM expects to see a negative fuel tank pressure (vacuum) within some range caused by the cooling of the fuel in the tank.