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This is actually a "known problem" and GM has issued an updated version of the EVAP canister vent valve assembly, as well as a "kit" that will re-locate the filter box. You'll need to obtain the kit which will contain everything you need to correctly repair this, as well as instructions for the re-location. 2004-2007 Model Year (Use Service Kit P/N 19152349)
It's located under the vehicle, on the driver's side, towards the rear.
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