Oxygen Sensor Bad In 1996 Pathfinder

I was cleaning out the engine bay the other day (carefully) but when I was finished I had a check engine light with 3 codes; both front oxygen sensors on the exhaust manifold and a knock sensor. So is it possible that the oxygen sensors are just bad or do you think that something got screwed up when cleaning the engine bay? Is there a fuse or something that I could possibly check? If it was your car what would you check first? I looked around and all the connections seemed to be okay for the oxygen sensors (I dont know where the knock sensor is). Thanks!!!!

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