Subaru Other

I have a 2001 Subaru outback wagon, 4-cyl 2.5L, 4wd. I just failed my smog test. The results showed 2 obd codes, p1133, and p0325. I searched these codes online. My results were; p0325, the knock sensor, and p1133, the rear o2 sensor. I have replaced both of these sensors, and when I test with an OBD reader, the p1133 still comes up as a fault code. Is there more than one o2 sensor on my vehicle? Or do I have an additional problem? Or, should I drive a while and try to reset the " check engine" light again?
September 12, 2007.

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