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Q: Check engine light code P0420

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my check engine light came on after I filled gas. I got the code read and it was the code P0420 for catalytic converter. However, after I drove it a couple times the light went off. I filled gas, it went back on and as before after driving a couple times it went off. Why would it be going on and off if there was a problem?

My car has 65000 miles.
My car has an automatic transmission.

A: You may have a purge valve that is leaking ...

You may have a purge valve that is leaking and causing excessive fumes to enter the intake manifold during the refuel process. When you start the vehicle, the excessive rich mixture may be causing the catalyst to overheat which will trigger the P0420 code. This will happen if, after a couple of starts, the computer does not see a problem and clears the code.

I'd recommend seeking some assistance from a certified mechanic who can diagnose your Check Engine Light first hand and fix the problem accordingly.

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