You may have a worn out Catalytic converter, not a sensor issue, this code almost is always the Catalyst (code P0720) not the sensor. If the sensor doesn't cure the light after reset and driving then the car is worn out, The downstream (after the catalyst) sensor is known as a "catalyst efficiency monitor"
P0303 is a misfire engine code for #3 cylinder, what that may be will require diagnostics, it can be a coil or even a computer, wiring or engine issue like a burnt valve. Fix the engine misfire and then clear and see if the code P1505 comes back, if it does you have a defective O2 sensor.
FIX MISS FIRE CODE P0303 IN CYLINDER 3
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