I have a '97 vehicle that may have had a bad catalytic converter causing the check engine light to stay on. After clearing/resetting the check engine light, I drove the car 90 miles. With this tool I could see when the car was ready for the smog test and it showed me what was wrong so I could fix it again for the smog test. Good handy diagnostic tool. A little expensive but it's very durable and useful especially if you have 2 or more vehicles :)
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