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I have a check engine light on and codes P0171 and/or P0172. Do I need a new O2 sensor?

The short answer is no likely. Those codes are not saying the sensor is bad.  When trying to diagnose check engine lights, some codes are more clear cut than others.  If you get a P0171 or a P0172, the computer is trying to tell you that reading the 02 sensor is not a problem, the reading itself is. In other words, the main computer (PCM in this case) is waving a red flag saying that a sensor is sensing some funky exhaust.  The reading is too lean (i.e. too much air or not enough fuel). P0171 is a bank one reading lean, P0172 is for bank two reading lean. If the PCM is saying is that the sensor cannot be sense, that would be a different code.  While there are always exceptions when dealing with computers and automotive technology, most likely cause would be air leaking in from your intake through a gasket or hose.  Technically air leaking through a gasket is called an unmetered air leak, the common term is a vacuum leak.  Looking for that vacuum leak can be the hardest part of the job.  From visuall inspection to using water, it depends on the application.
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