OBD II codes on Buick??

Buick Park Ave, 2003, just threw a "Service Engine Soon" message and my OBD reader says "Evaporative emissions system leak detected (small leak)". So just what does this mean?? Are there any web sites that might explain this?
Thanks

My experience on that one, first make sure the gas cap is sealing properly.... Second, there is a solonoid in the rear, near gas tank, that releases pressure on ocassion, when called upon by the computer, have had to replace that one. Last time, I got the wrong one to replace, and on a Sunday afternoon, the auto store was closed. Took old one off, disassembled, cleaned out with WD-40, especialy the litttle foam air filter. Reassembled - put back on, worked well, until car went into the gerat junkyard in the sky.

(quoted from post at 04:26:10 06/05/11) My experience on that one, first make sure the gas cap is sealing properly.... Second, there is a solonoid in the rear, near gas tank, that releases pressure on ocassion, when called upon by the computer, have had to replace that one. Last time, I got the wrong one to replace, and on a Sunday afternoon, the auto store was closed. Took old one off, disassembled, cleaned out with WD-40, especialy the litttle foam air filter. Reassembled - put back on, worked well, until car went into the gerat junkyard in the sky.

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Just went through this same scene with my 97 Lesabre limited. The same code and I just ran it with the light on for a while and one day it cleared and hasn't came back on, It came on after my wife had filled it with gas and I suspect a loose cap was the issue. It did not clear immediately upon tightening the cap but did and is working well with no more codes. It turned 254,000 last week on a trip to N.C. from Penna. and all is well. mEl

Code PO440? Usually a loose or worn out gas cap.Check to make sure the cap doesn"t click too easiily and the rubber seal isn"t cracked.

Actually the code say PO442
What does this mean?

Yes it might be the gas cap. I checked and it was installed with only 1 CLICK on the ratchet. I've now re-installed it with about 5 clicks on the ratchet and cleared the error code, so I'll see over the next few days whether the code returns.
Thanks for the replies

Gas cap loose will usually do that on a GM! After it happened 3 times to me, I tend to remember that one! LOL

On our 01 it turned out to be the little sensor at the end of the filler neck that tells the dash the cap is loose. Glad it was still under warranty then, but its done it again now, I just tell the wife to ignore it. 302000 and some change on it.

P0xxx are standard codes shares between all vehicles made for US after 1996. P1xxx are model specific codes.

Note - Vehicles made outside the US, not for import to the US did not go to this standard until 2000-2001. Plus some diesel models do not follow the standard codes.

I found this to be one of the better links to get info from. Scroll down to see standard codes. Click on a manufacture to see specific codes.

Codes P0442 - http://www.obd-codes.com/p0442

Technical Description - Evaporative Emission Control System Leak Detected (small leak)

What does that mean?
This indicates a fuel vapor leak in the EVAP control system. It means a very small leak has been detected. In fact, the leak can be from a hole as small as 0.04" in diameter. The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage. Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

Symptoms
You likely won't notice any drivability problems.

Causes
A code P0442 most likely means one or more of the following has happened:
•A loose or improperly affixed gas cap
•A non-conforming gas cap (i.e. not factory/original brand)
•A small leak/hole in a fuel vapor hose/tube
•Other small leak in EVAP system
•Faulty vent o-ring seal

Possible Solutions
With a P0442, the most common repair is to:
•Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back.
•Otherwise, replace the gas cap, or
•Inspect the EVAP system for cuts/holes in tubes/hoses
Trouble codes