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Q: Check engine light came on, took to Autozone, diagnosis is Evaporative Emissions Canister.

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What could cause the EVAP canister to fail? The sheet from autozone says "before replacing, determine and repair the cause of the problem. How do I do that? I am no mechanic, but am able to do a several things. Should I just replace the canister? Thanks for your help

My car has 80000 miles.
My car has an automatic transmission.

The EVAP canister is simply used to store fuel vapors until the engine control module is ready to burn the fuel vapors in the engine. Although the EVAP canister can fail, it should not be replaced without a proper diagnosis of the entire EVAP system. In order to accurately test the EVAP system, you will need an EVAP leak checking tool, usually a smoke machine designed to find any leaks in the EVAP system. You will also need an advanced scan tool to verify diagnosis, check operation of certain components, and view certain parameters for the EVAP system. You should have a qualified technician, such as one from YourMechanic, diagnose the check engine light and suggest the appropriate repair.

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