2000 Honda Civic Check Engine Light

I got a oil change and a coolant replacement done at the dealer and drove home roughly 5 miles. In the evening ( afer 6 hours) when I started the car the check engine light was on and the engine was
vibrating at the idle speed. Then I took the car back to the dealer and they connected the diagnostic computer and found out that the oxygen sensor is bad. The mechanic cleared the alarm and the engine started running normal. They advised me to get the sensor replaced which costs around $300. I am just wondering how the sensor could go bad right after the service. Is there anything that I can do to find out whether the sensor is really bad?
Thanks, Ken
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out of, place? Price the sensor somewhere else. Parts stores carry some of them.
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