[QUOTE=randy_k;6696166]
Quote:
Originally Posted by JFP in PA
The canister itself is a passive device; what cause the codes and other issues are either failed valves that control the vapor flow to and from the canister, or blocked lines that prevent the vapor flow, or lines that become disconnected and cause vacuum leaks into the intake system.
The canister is a charcoal filled chamber that absorbs and stores fuel vapor from the tank and then vents it into the intake system to be burned when appropriate. All the rest of the hardware just moves the vapors around.
QUOTE]
So JFP. When it gives us the code.
P0446:
Shutoff valve activated charcoal filter (function) below limit value
Does that mean that the vapor has turned to a liquid or the charcoal filter is clogged to the point it won't operate correctly? I think that is what you mean. Like an air filter that gets clogged full of dirt. Just checking and it may help others on here to understand what it does. Not trying to over think things. Or bug you. But I love knowledge of how things operate and why.
I tend to research the crap out of everything. Well except my first wife. 
Hope all is well in PA.
Randy
Randy |
OK, let’s see if we can clear up any confusion.
The EVAP canister is a plastic container full of activated charcoal granules (much like the ones used to clean the water in a fish tank filter). Their purpose is to suck up and trap hydrocarbon vapors from the fuel tank and hold them until the system opens the purge line and sucks them into the intake system to be burnt. This process eliminates any hydrocarbon release from the fuel system to the atmosphere. The EVAP canister does not see liquid fuel; it is a vapor only unit.
The canister shutoff valve closes to seal the purge air line to the EVAP canister while the system is running the fuel tank leak test (a pressure test to verify that the fuel system is totally sealed from the atmosphere). When the system is running the pressure test, if either the purge air line is blocked, the shutoff valve has malfunctioned, or the resistance to airflow in the EVAP canister has become too high (due to contamination or the charcoal breaking down and clogging the passages), the car will throw the P0446 code.
Diagnostic procedure is to check the purge air line and canister purge valve for blockage or malfunction; if blocked, blow it clear or replace it. If the line and valve are OK, the EVAP canister has to be changed out, it is not serviceable.