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Q: Evap large leak code

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My car is not passing emission test due to code P0455 on my car. I have changed my gas cap since that's what everybody is telling me to do first. After I changed the gas cap, I have deleted my code to check if it will come up again and it did. I have NO engine check light on my speedometer. Now I'm not sure if to change my purge valve solenoid or vent valve solenoid or my charcoal canister. Please I need an advise/solution.

My car has 161000 miles.
My car has an automatic transmission.

If you have a large emission system leak the best way to find the leak is to do a smoke test and put smoke pressure in the fuel tank and it will show the smoke out of the system leak. The most common leak besides the fuel cap is the purge or vent valves. This test will pinpoint the valve that is leaking so it can be replaced. If you have no smoke machine then use a vacuum pump to check the purge valve to see if it holds vacuum? If it does not hold vacuum then replace valve.

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