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Q: OBD II shows front upstream O2 Sensor is bad. on 2003 Toyota Highlander

Parts available give me two choices. O2 sensor and Air Fuel Ratio sensor. Which is it? Location is Front manifold pre cat.
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was it 'Toyota' or aftermarket 'parts' that asked you that question?I'd bet it was advance or autozone. It's an a/f sensor pre-cat , O2s , after (or in middle) of cat (downstream). one is for engine management the other is for emissions monitoring.(short explanation). Safer and less costly to keep your Toyota , all Toyota!!
Okay so you are saying manifold location pre-cat its called an a/f sensor and post cat its called an o2 sensor right?
Yes and I'm also stressing the importance of an OEM part. (I understand the $ difference for what should be the same part , but they're not). As I said in my first response they perform different functions.
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