I'm chasing ocassional P0440 OBD code. Did some research and understand what can cause it. What I don't understand is this, Once EVAP system is under pressure which component will actually detect the leak? I don't think it is the purge valve...It obviously has to be some electronic sensor. Is there one in or near the gas tank?
This is why I don't think it is the purge valve...Let's say there is a major break in one of the vacuum lines that's not allowing pressure to build. How is that different from time when purge valve opens, or is stuck open? Result is the same, lack of pressure...
Or let's say purge valve is stuck closed, and we have a constant pressure. Why would CEL get set??? Does this mean CEL is only set if the purge valve is stuck open, or if ther's leak in the lines? Aspirin anyone???
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