Check engine light on in my 97 Maxima. Knock Sensor?

Autozone ran a diagnostic and 2 of the 3 problems came up as knock sensor issues. The third was an emissions problem that the guy said was insignifigant. He recommended putting a pint of Sea Foam in my next tank of gas, which I did, but did not solve the problem. I do not know much about cars. Does this mean that... show more Autozone ran a diagnostic and 2 of the 3 problems came up as knock sensor issues. The third was an emissions problem that the guy said was insignifigant. He recommended putting a pint of Sea Foam in my next tank of gas, which I did, but did not solve the problem. I do not know much about cars. Does this mean that the knock sensor needs to be replaced, or that the sensor is identifying a problem in the engine? Also, I just noticed the other day that there is a sticker by the gas cap that recommends using premium fuel. I have been using regular. Could this be part of the problem? Is premium fuel really necessary for this "not-so-high" performance engine? Thanks in advance for any advice.
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