1998 Toyota Camry O2 sensor

Yes, could be a downstream O2 sensor. To learn how to check an oxygen sensor, follow the link below.

https://www.2carpros.com/how_to/how_to_test_oxygen_sensor.htm

If all O2 sensors are OK, need to have catalytic converter flow tested.

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You say code P1133. You mean code P0133 or is it California emissions vehicle?

Code P1133 indicates a Air/Fuel Sensor (AFS) circuit response malfunction.
The AFS is located in each exhaust manifold. You can use an ohmmeter to measure resistance between Black wire and Black/Red wire (bank No. 1) or between Black wire and Black/White wire (bank No.2) at the AFS connector. Resistance should be.8 - 1.4 ohms at 68F (20C).

If the code is P0133 then the bank No.1, sensor No.1 needs replaced. This sensor is the one located on the side of engine that includes cylinder 1. The sensor No.1 refers to the sensor closest to the engine block.

I always suggest using OEM parts on vehicles. They last longer and perform better than any other brands. Of course, they do cost more so you will have to judge which one you want.

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