Q: bad o2 sensors

Diagnostic Trouble Codes can never be used to "directly" condemn parts. In the case of an oxygen sensor, the oxygen sensor output must be evaluated on a scope to determine if the sensor itself is bad or if you perhaps have a situation where there is simply a loose wire or other fault in the circuit (or even a fault in another unrelated engine system). If the oxygen sensor output was not evaluated on an automotive scope, it might have been a perfectly good sensor and thus the problem lies elsewhere. If a diagnostic was done, and the sensor is out of spec. then it should be replaced. As far as the knock sensor is concerned, the exact same technical instructions apply. If the output of the knock sensor was tested and it tests bad, replace it. If it tests good, keep it. If it was not tested, then you have no information upon which to make a decision because codes are not a diagnostic. Codes provide clues and sometimes the clues aren’t even that great. If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a check engine light diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.