The sensor that reads pressure is screwed into the oil filter elbow off the front cover. Might make sure the sensor is plugged in, and/or the wires are not cut or damaged. If your oil light is on, then the sensor is reading 5psi or something like that, and by then, its usually too late to save the engine. It could be damaged or broken too.
The sensor in the pan is your low oil level indicator, rarely do they go bad, but they can get damaged sometimes.
Your oil level was VERY high when we worked on your car, it was over filled, now its low? Did you drain some out, maybe drained too much out possibly?
As for the O2 sensor, Denso's are nice because they tolerate leaded race gas. You can run them, they do work, but they don't last long, especially with race gas being ran. Delco sensors will sbe just fine, a exhaust leak will screw with your readings, because thats un-metered air being introduced. I think you need to do some fixing on your Pace Setters, and then see what happens. But also check your sensor wire(s) for possible melting, that happens.
My car has a check engine light for the O2 as well, it works fine, scans fine, it just doesn't agree with the PCM for some reason. LOL Might just be a '97 bastard thing too, who knows.
~F~