1999 Boxster Po446

[RichardB]

I'm sure this has been answered before, but I'm not getting much info when I do a search on it.

Took my boxster in for its annual inspection and it failed. (The check engine light was burned out too!!!!)

PO446: Evaporative Emiss Control Sys. Vent Control Circuit Malfunction.

Any ideas where to start or what this might be?

Thanks,

Richard

[Loren]

:welcome:

Search is your friend.

http://www.renntech.org/forums/index.php?/topic/31181-p0446-code-and-no-vacuum-in-fuel-tank/page__view__findpost__p__165450

[RichardB]

That is the same diagram that I have studied in my maintenance manual. It is a really poor picture that doesn't tell you much (not detailed enough).

Does anyone know which of the three lines attached to the evap canister is the purge line? There is one on top, and two on bottom. Of the bottom ones, there is one towards the rear of the car and one toward the front of the car.....

Is there a check valve on any of the lines?

Thanks!

Richard

[Loren]

Purge air is line near the number 6 on the diagram. Attaches near the top of the canister towards the fuel filler.

[RichardB]

Strange because that line flows just fine. Blew through it with my mouth and then an air compressor with no problem.

Richard

[RichardB]

Something else strange.... The purge valve works when I apply 12v. When I read the output voltage going to it, I only get 6.66 (appropriate....)

I'm not sure what triggers it to go to 12.

Any other ideas on what might be causing the error? The carbon canister itself??

Richard

[RichardB]

On the EVAP system there are two solenoids and one pressure sensor. I have found the Solenoid that attaches to the carbon canister, and I have found the differential pressure sensor. Does anyone know the part number or where I can get the solenoid that is under the intake manifold?

I suspect this one is the problem. It is a normally closed valve and when I put power to it, it will open. When I remove the power it will close.... (seems normal right??) When I turn off the power supply instead of removing the alligator clip the valve stays open...... I suspect that when the power bleeds off instead of shutting off immediately the valve sticks.

Any thoughts? Got a part number?

Richard

[RichardB]

Part number was 996-110-129-05. I will post if it worked.....

[txhokie4life]

That is the same diagram that I have studied in my maintenance manual. It is a really poor picture that doesn't tell you much (not detailed enough).

Does anyone know which of the three lines attached to the evap canister is the purge line? There is one on top, and two on bottom. Of the bottom ones, there is one towards the rear of the car and one toward the front of the car.....

Is there a check valve on any of the lines?

Thanks!

Richard

from the valve hosing in the front. the side line vents to air. The second line goes the the evap canister -- I think the 3rd line goes to the fuel tank which

then there is a line that heads to the back of the car. -- maybe this line is the one that heads back to the engine... I never traced it completely.

I spent a month tracking down a similar problem and replaced everything -- finally replaced the EVAP shut off valve (back by the engine) and now it works perfectly.

Try that one first -- might save you $300 in parts and a ton of shop time.

Mike

[RichardB]

UPDATE - RESOLVED

Mike, thanks for your reply. I had ordered the EVAP shut off valve (which is underneath the left intake manifold) about an hour before your post. Your email helped make me feel better about the decision. Gratefully, that is what actually fixed the problem!

The line from the intake manifold connects to the top of the fuel tank through the differential pressure sensor. There is a line from the gas tank to the bottom of the carbon canister (I think the connector towards the rear of the car). The other connector on the bottom connects to a mechanism on the filler neck. The line that attaches to the top of the carbon canister is the vent line that for some strange reason goes all the way to the back of the car (maybe to keep the fumes to the rear?).

The solenoid on the carbon cannister is a normally open device.

The solenoid under the intake manifold is a normally closed device.

You can use a 9v battery (with alligator clips) to actuate the valves.

For a vacuum (or pressure, but be really careful with pressure!!!)test you would close the valve on the carbon canister to make sure there weren't any leaks in the lines.

In my case all the solenoids worked just fine. I had a variable power supply that I set for 12 volts and used it to actuate the EVAP shut off valve under the manifold. When I connected or disconnected the alligator clip, the solenoid always closed immediately. When I left the alligator clip attached and instead just turned off the power supply, the solenoid didn't always close. (I had a hose connected and was blowing air with my mouth through). I am guessing that as the power bled down instead of immediately being removed the solenoid would stick.

What a really fun experience. (ok, not really). But, while baby was up on jack stands, she got new plugs, new filters and an oil change.

Thanks all!!

Richard

Edited April 18, 2010 by RichardB

[txhokie4life]

UPDATE - RESOLVED

Mike, thanks for your reply. I had ordered the EVAP shut off valve (which is underneath the left intake manifold) about an hour before your post. Your email helped make me feel better about the decision. Gratefully, that is what actually fixed the problem!%

As much as this board has helped me -- it's nice to give back!

Mike