P0446 Evaporative Emission Control System Vent Malfunction

[e7ats]

e7ats
Posted: May 22 2006,10:35

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Ok James, Need a little help with this one.
2004 AWD Safari, Code came up around 46,000 Miles and it is now at 77,000 miles. The SES light is driving me nuts. Any ideas on this one?

P0446 Evaporative Emission Control System Vent Control Circuit Malfunction

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V8famvan
Posted: May 23 2006,9:42

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Yeah, I noticed the mileage. Nothing like jumping right on it.

Anyways, What will cause that code to set is the PCM draws a vacuum on the fuel tank & then seals the system. (Closes the purge & vent solenoids) When it runs the test for code P04446, it opens the vent solenoid & then monitor the fuel tank pressure sensor drop rate. If the drop rate is too slow, the code sets. It basically assumes there is a restriction in the vent system that is blocking the release of pressure from in the fuel tank. It has to pass alot of other codes to be able to fail this one, so alot of other stuff/items are good. IE: No leaks in the EVAP system.

Common causes:
Easiest
- Dirty filter in the evap vent solenoid. Remove & check the solenoid. Commonly they accumulate dust in them. Clean it out & check the flow by blowing thru it while energizing it.

Most common
- Another thing I have seen is a faulty pressure sensor on the top of the fuel tank. This is the sensor that the PCM uses to monitor the vacuum drop in the tank, so if it is out of calibration....You get the idea. Typical voltage reading from the pressure sensor is 1.5 volts at ambient pressure (gas cap off). If you are not getting this reading at ambient pressure, replace the sensor.

Least likely
- Restricted charcoal canister. The fine dust makes it's way thru the vent solenoid & filter & accumulates in the charcoal of the cainster. Check the nozzle on the canister that goes to the vent solenoid for fine dust in it. Or try blowing a little bit of air into the said nozzle & see if fine dust blows back out at you. If there is too much dust in there, you must replace the canister.

Hope this helps you somewhat.
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[e7ats]

I have not had time to check into it anymore than using a scan tool to turn off the light. Something I did find out was if I let the van warm up 2 minutes before driving the code will not set. If I drive cold the code will set.

[v8famvan]

Ok, I recently had a run in with a '99 Blazer that had this code reoccurring. It had come into the shop 3 times before I got a crack at it. Ended up being a charcoal canister. I cut the canister open & found a section of the charcoal pellets in there had bonded together because some water??? got in there. Since the charcoal pellets had bonded together, the air would not flow thru that section very well. Normal vacuum 'drop time' was less than 10 seconds. This one was at 14 seconds. Not much off the mark. Changed with a new one & the problem was solved. Vacuum drop time went to 9 seconds & all was ok.
So how do you feel about doing a quick swap-a-roo with the work truck? If the problem switches vehicles......
I think you get where I am going with this.

[e7ats]

Where is the charcoal canister located? Yes you do have to tell me everything.

Also what is that big black container on top of the fuel tank? I hope that isn't it.

[v8famvan]

LOL!
Yes that 'big black container' is the charcoal canister, sorry but you do have to drop the tank at least some to remove it. They used to be easier to remove.