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Check Engine light on,2002 Hyundai

Just returned from “Auto Zone” parts company…My check engine light is on…They determined that the problem was trouble code PO133… “Oxygen Sensor Defective”…What should my next step be? Thank you

It doesn’t actually mean that the O2 sensor is defective, though that is one possibility.

Have a look at this link to get started:
http://www.obd-codes.com/p0133

As previously noted, it does not mean “Oxygen Sensor Defective” It does mean it has detected an unexplained signal from that circuit. I might be a bad sensor, but it may be a loose wire … etc. It is at this point where the mechanic needs to intervene and determine exactly what is happening.