Charcoal Eavap Canister Shut-Off Valve
08-29-2011, 11:09 PM
#1
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Charcoal Eavap Canister Shut-Off Valve
I've posted here (W203 Forum) regarding my P0446 DTC on my 2002 C320 Wagon, and today I removed the Charcoal Canister Shut-Off Valve, which is mounted on my charcoal canister, from my car to examine, clean, and test it.
The valve is squeaky clean, and when manually activated (pushing on the pindle), seals perfectly, and isn't sticking.
I read (All Data) that the valve should draw 0.4 to 0.9 amps (though I do not know the operating voltage or when it is activated).
I first measured the resistance of the valve's coil itself using a VOM to check for continuity, and it measures only ONE ohm.
I found an "All Data" test procedure for the shut-off valve in a ML 320, and while the valve is self-contained on that model, and is not part of the canister, I assumed that it is electrically similar. It said that the valve can be tested using 12volts for under one second duration.
When I do that (observing the polarity stamped next to the valve's pins), the valve does NOT activate (nor does it remain activated if I first hold the pintle closed before applying the voltage).
The current is high (I would expect 12 amps with one ohm at an applied 12volts via Ohm's law), and heats the 20ga test leads even with a momentary contact to the pins.
I assume I have found the reason for my P0446, unless my test was way out of the ball-park. Further non-destructive disassembly/repair of the valve body appears impossible.
My concern now is what that one ohm (close to a dead short) may have done to harm the electronic control circuitry of my vehicle (vehicle computer).
Beside replacing the valve, what can I do to test the circuitry?
WHEN exactly is voltage applied to the shut-off valve to close it? Or is it normally closed, and opened only to relieve excess tank pressure? If I knew when to look for activation voltage at the valve's connector pigtail, I could be reasonably certain a repair has been effected.
Are there any fuses protecting this circuit from high current draw or a short (as my valve appears to be mimicking) that I should check?
I don't want to install a new valve, replace the fender liner, and then find that I have to get under there again for further troubleshooting.
Any help appreciated...
Many thanks,
Bob
The valve is squeaky clean, and when manually activated (pushing on the pindle), seals perfectly, and isn't sticking.
I read (All Data) that the valve should draw 0.4 to 0.9 amps (though I do not know the operating voltage or when it is activated).
I first measured the resistance of the valve's coil itself using a VOM to check for continuity, and it measures only ONE ohm.
I found an "All Data" test procedure for the shut-off valve in a ML 320, and while the valve is self-contained on that model, and is not part of the canister, I assumed that it is electrically similar. It said that the valve can be tested using 12volts for under one second duration.
When I do that (observing the polarity stamped next to the valve's pins), the valve does NOT activate (nor does it remain activated if I first hold the pintle closed before applying the voltage).
The current is high (I would expect 12 amps with one ohm at an applied 12volts via Ohm's law), and heats the 20ga test leads even with a momentary contact to the pins.
I assume I have found the reason for my P0446, unless my test was way out of the ball-park. Further non-destructive disassembly/repair of the valve body appears impossible.
My concern now is what that one ohm (close to a dead short) may have done to harm the electronic control circuitry of my vehicle (vehicle computer).
Beside replacing the valve, what can I do to test the circuitry?
WHEN exactly is voltage applied to the shut-off valve to close it? Or is it normally closed, and opened only to relieve excess tank pressure? If I knew when to look for activation voltage at the valve's connector pigtail, I could be reasonably certain a repair has been effected.
Are there any fuses protecting this circuit from high current draw or a short (as my valve appears to be mimicking) that I should check?
I don't want to install a new valve, replace the fender liner, and then find that I have to get under there again for further troubleshooting.
Any help appreciated...
Many thanks,
Bob
