What is code P2238?

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The check engine light came on at 184000. I brought to a dealer and was advised that catalytic converter needs to be changed. I went to a mechanic and changed the catalytic converter for a cheaper price. Now the mechanic said that check engine light will still come on and said he will just reset it. The light came on again and he reset it. After a couple of days, the light came on again, he said it has a code P2238. Is this right?