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2001 STS
2001 STS
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417 Posts
Discussion Starter #1
Last fall my 2001 STS was showing "Check Gas Cap" and code P0440 (evap leak) is present, no other codes. So I replaced with gas cap with a new OEM one and problem went away.

Now in spring the message and same code are back. I have:
1. Cleaned and tested purge valve
2. Cleaned and test vent valve
3. Looked for obvious hose leaks

Being in Canada it will cost me $130 for a leak test (smoke test)...which exceeds the price of any of the above parts. Before I hand GM the cash, can someone suggest a likely cause and solution?

Do vent valves fail intermittently? (Just guessing)
 

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02 Seville, 04 SRX
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1,347 Posts
There is a diagram of the vacuum lines somewhere on here. You need to check all those. The other part that you can't see, is where it attaches in the intake manifold. If you remove the intake manifold to do an inspection, you need to have a new gasket kit ready to go when you reinstall it. I can't remember, but the plenum may also cause the error code. you can check that by idling the car and then spraying that rubber part with Braklean. If it studders, there is a rip in the plenum.
 

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2001 STS
2001 STS
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417 Posts
Discussion Starter #3
The purge valve connects directly to the throttlebody, and gasket on valve looks good (I pulled it for testing).

I've replaced the plenum twice, but that problem shows trim levels out of whack, and they look fine now. So I think it's pointing to something else.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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69,475 Posts
Here's your EVAP drawing. The charcoal canister is on the frame rail about under the driver's side rear seat area.

Check the test port cap - a green "valve cap" near the brake booster - on the EVAP purge line.

2002 EVAP.gif
 

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2001 STS
2001 STS
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417 Posts
Discussion Starter #5 (Edited)
That green cap is on tight (is that all there is to a "test") ?

BTW, I removed the vent valve, took it apart and cleaned it, lubed with silicone, etc...and tested that it worked fine.

I think the PCM would set codes for purge/vent seperately, so P0440 means general leak. (If my understanding is correct).

Learning towards buying ANOTHER gas cap...but I if there's something I can test before I throw away another $35 then would be happy
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
Joined
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69,475 Posts
There's a vacuum test set that connects to the test port. A Tech-II then commands purge/pressure/vent events for function testing.
 

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2001 STS
2001 STS
Joined
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417 Posts
Discussion Starter #7
Unfortunately I don't have access to a tech 2. I tried commanding them open/close by applying 12v and confirming they sealed properly. But not fully connected, and not holding a vacuum....getting to the limit of DIY.

Anything else I can do? (I found a great article about DIY smoke test by burning leaves in a bottle and connecting to filler neck - haha)
 
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