P0446 Evaporative Emission System

[FXRseen]

Hello I have a 1998 AWD Astro Van. My check engine light is on and the code is P0446.

Information I know.

Definition:
EVAP purge/vent solenoid circuit condition.

Explanation:
The solenoids and system wiring are monitored for opens or shorts.

Probable causes:
1. Purge or vent solenoids defective. (Where and how do I fix this)
2. Check connector and wiring.
3. Fuel saturated vapor canister.
4. Failed EVAP vent solenoid. (Where and how do I fix this)

Information I found on old Forum.

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 P0446, 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.


This is all good information. So is the first thing I should check is the "filter in the EVAP Vent Solenoid". Where is this located? Where is the charcoal canister located? Is there a better checklist that I can do to fix this problem?

['cudapaul]

The first thing to check is the gas cap.

There is an "O" ring that seals it to the filler neck.
If it is cracked, broken, or missing, it could be as simple as that.
Some locking caps can develop a leak, even with the o-ring intact.

[Matrixx]

Hi FXRseen
The first thing I would check personally is the gas cap. If you get any pressure released from it when you remove it is a good sign the cap is faulty and it should be replaced. Any rust around the inside of the gas cap, then the cap should be replaced. If you choose to replace the gas cap, this needs to be "very" application "specific".

In other words, an OEM cap is my only recommendation here. I had to replace mine and the dealership had a hard time finding one that matched the required Specs. needed for these vans. He had to cross reference it to a newer full size truck (which I can't think of the name at the moment) and that was the only vehicle that matched the specs. for my gas cap.

-The EVAP Purge Solenoid is a square type box located on the front drivers side intake manifold. It's held down by 2 - 10mm bolts with a 2-wire plug-in and vacuum lines leading into it. It's not repairable. It must be replaced as a unit if it's faulty.

-That would be the 2 - wire plug-in already mentioned.

-The Charcoal Canister "should" be located on the passenger side rail with 3 - vacuum lines hooked up to it. (purge line,fuel vapor line and air line).

-The Evap Canister Vent Valve is located on the drivers side rail close to the fuel filter right next to the G302 Ground wire bolted to the rail itself. Their will be a vacuum line and a plug-in hooked up to it.

Hope this helps. Please keep us updated, Thanks.

[Matrixx]

Hi cudapaul

Hey, you weren't their when I was writing my post up. Interesting how we came to the same conclusion for the first thing to check. I didn't even see your post until I submitted mine (just to clear that up).

[FXRseen]

Nice thanks for the tips. I've already replaced the gas cap with a Autozone locking cap. I've had gas stolen out of my van several times and I've been meaning to get one that locks. Still the CEL didn't go out on the way home. Maybe it takes longer if that is what it is. I will start checking the items listed for proper condition thanks.

[Matrixx]

Hi FXRseen
You can clear the code yourself if you like or Auto Zone should be able to do it for you. Just disconnect the Negative post on the battery for a couple of minutes then hook it back up. You will have to reset your radio though, so it's your choice. Once you have cleared the code, and if the SES light comes back on again, then check the other components mentioned above. Please keep us updated, Thanks.

['cudapaul]

If you don't want to disconnect the battery, you can pull the fuses labeled ECM-I and ECM-B.
This will remove power from the ECM (computer) and clear the codes.

Or buy a ScanGauge and do it while you are driving!

http://www.scangauge.com/

[gtkane]

Just to note, that the gas cap remedy mentioned is actually a fix for p0440, and not p0446.

[FXRseen]

Well I replaced the purge solenoid and the CEL has not shut off after driving for 15 minutes on the freeway. So I'm not sure yet if it still has a problem or not.

I also checked out the vent solenoid and it seems fine. It's suppose to be closed under normal conditions and it was. Also the charcoal canister was clean of dust. It did though have liquid in the large vacuum line but not much. I could blow air easily through the vacuum ports. I'm not sure what to check now.

[Matrixx]

Disregard, I understand your reasoning for the drive cycle, the codes still need to be cleared after that though the way I or cudapaul suggested, your choice.Hope this helps.Please keep us updated, Thanks.

[FXRseen]

Well I want to give an up date. I checked the charcoal canister and it checked out fine as I listed above. I ended up replacing "The EVAP Purge Solenoid" as listed above. I chose to do this part change without checking it because it was the only part that the chevy dealership caries. So after changing it I reset the computer and it's been a couple of weeks with no CEL. I hope this did it and I'll update further if there is another problem. Hope this helps someone.

[FXRseen]

Still no check engine light this must have fixed it.

[Matrixx]

Hi XRseen

I'm glad you found the problem, Thanks for the update.

[spongebob218]

I don't know how I missed this post. The vent valve is one of the most commonly replaced items on any GM truck/van/suv, even more so than gas caps. They are normally open(venting to atmosphere) and close when commanded by the PCM. A P0446 means the valve was stuck closed. The vent valve could also set a P0455(large leak) if stuck open, or a P0449 if the PCM detected a circuit problem(short, open). They are usually full of dirt/road grime and seem to be safe havens for spiders. Some of the newer trucks even have a bulletin about relocating the breather for the vent valve to the top of the transmission by means of a long piece of heater hose to prevent dirt from entering the valve.

[RootsMan]

I don't know how I missed this post. The vent valve is one of the most commonly replaced items on any GM truck/van/suv, even more so than gas caps. They are normally open(venting to atmosphere) and close when commanded by the PCM. A P0446 means the valve was stuck closed. The vent valve could also set a P0455(large leak) if stuck open, or a P0449 if the PCM detected a circuit problem(short, open). They are usually full of dirt/road grime and seem to be safe havens for spiders. Some of the newer trucks even have a bulletin about relocating the breather for the vent valve to the top of the transmission by means of a long piece of heater hose to prevent dirt from entering the valve.

Where would the "vent valve" be located on a 2003 Chevy Astro AWD?

Thanks,