my check engine light is on says cats are bad looked at the exhaust cat and looks good
2 Answers
physically looking at it doesn't mean its good. It's what's on the inside that counts. You will likely need to replace the entire cat. converter. Just a heads up, they are expensive ($200-900 if you include labor)
Temperature measurements are one way to diagnose a bad cat. https://www.2carpros.com/articles/how-to-test-a-catalytic-converter