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Replacing the gas cap as suggested here worked for about a week. But now the check engine light (evap code) continues to re-appear. This is about the third time in three months the check engine light has appeared. Each time the code is EVAP CODE. I don't know if there is more than one evap code. This is what the mechanic told me. All my mechanic has done is reset the light. What else can I do besides replacing the gas cap to prevent the EVAP CODE from appearing? This is for a 2001 Toyota Sienna.

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up vote 2 down vote accepted

In an answer to your linked question, Larry suggests that the indicator light could be coming on due to a loose gas cap, a torn hose or a leaking seal. Remember how the system works:

When the right conditions are met IE fuel level between 1/3 and 1/2 tank, outside temp 50 - 90 etc. the ECM pulls a vacuum on the evap system and makes sure it holds a vacuum. This tells the ECM if there is a leak, allowing vapors to leak into the atmosphere. If it fails this check x number of times it turns the MIL (malfunction indicator lamp) on.

So anything that causes the fuel system to fail to hold vacuum could trigger the code. The fact that replacing the gas cap wasn't sufficient doesn't necessarily mean that the cap wasn't bad. It might have been necessary but not sufficient to fix the whole problem.

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