Purpose of the knock sensor and o2 sensor

[versatilx1]

Well i had one hell of a time finding out why my check engine light was on, First probelm knock sensor no good, Second o2 sensor bad. So my question is how could of these sensors went bad(Lets keep in my mind just rebuilt the motor bottom end). And is it hard to replace these sensors?

 

[Burntz]

The o2 sensor should be pretty easy. Sometimes they are STUCK in there, and you might have to take a torch to where it screws in to get it hot and expand, so you can get it out.
- The o2 sensor monitors your exhaust for excess unburnt fuel, and will tell your car to recirculate the exhaust to be reburnt (EGR = exhaust gas recirculation), as to improve gas mileage and reduce emissions (Someone correct me if I'm wrong)

The knock sensor monitors for ping/knock, and will pull timing should knock occur. If its reading incorrectly, it could be continuously pulling timing and making your car run odd. I don't think these are extremely hard to replace either, but I'm just getting re-acquainted with DSM's

 

[boosteclipse]

Both are important, and luckily both are easy to change. As far as why the went out, I couldn't tell ya. O2 could be for many reasons.

 

[snakeyes711]

Well, a o2 sensor can burn out several ways. The knock sensor gets old, and the material surrounding its mic can turn to goo, and ooze out. However the knock sensor could be unplugged or have a bad connection at the plug terminal to trip the cel light. Or the wiring become oxidized, and fray bad or such. All in all both sensors together are around a hundred dollars. Not real bad money, but can really affect the how your car will run, from having no power, right down to the worst gas mileage you've ever seen.

 

[versatilx1]

Yeah my car has been feeling like as if its running at 50% really bad... And im happy to know that the sensors could be a big part of this dilema (Burntz) thank you that was very helpful. See im new to the whole sensors/electrical wiring so this question could be pretty basic to people , but better safe then sorry..