Knock sensor question

My car has been getting terrible gas mileage and has has horrible low end acceleration. I checked the ecu and is was giving me 0304 (Knock sensor). My mechanic was telling me not to buy a knock sensor right away since he claimed that the computer gives knock sensor codes whenever there is a misfire or anything in the engine. He said most of the time the knock sensor code doesnt even mean you need a new knock sensor. Is this true?

Yes it's true, but thats usually when the KS code comes up with other codes. If your only throwing the KS code and you have bad gas mileage and poor performance then your KS is probably dead.

For example if you throw the KS code with an o2 sensor code, replacing the o2 sensor will make the KS code go away 99% of the time.