fuel pump or 02 sensor? on 2000 Pontiac Montana

The computer testing reveals o2 sensor out. Infront part of car. We replaced fuel fiter. gas occassionally not getting up to engine, is pump gone? or is it o2 sensor? pump is way expensive, is it easy to replace w/o service manual? got 186000 miles we were hoping to get it to run another 100,000.

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1 answer
a common problem with this is the plug from the gas tank. it plugs into the floor just behind the driver's seat. the connections corrode in the plug and causes the pump to fail.