I understand all of this.
To my knowledge, if a O2 sensor goes bad, it will trigger a O2 sensor code. P0430 is says a catalytic failure of some sort. Am I incorrect in stating this?

This is where I am confused, especially being that my 04 LS has only 98k on it

 

I get a "Check VSC" light while the car is crankin when I turn the key and the exclamation with a beep goes on too. The light shuts off right after. It only happens once in a while. Is this similar to how you problems started ???

 

Nope, mine just went on, and stayed on. No flashing. I do, of course, have the exclamation point with the check engine and VSC

 

This code means: Either the catalytic converter is no longer functioning properly or an oxygen sensor is not reading (functioning) properly or there is an exhaust leak.

Specifically the "PO" means this is a standard code. The "4" means it's related to your auxiliary emissions controls and the "30" means it's probably a catalytic converter issue.

It's not unusual for oxygen sensors to fail or go off-spec after about 4-5 years of driving so, no, 98k miles is not unusual. Actually, it's pretty good.

 

Great. Per your reccomendation, which ones should I replace?

Any way to tell which side has gone bad?

Thanks

 

I'd replace both upstream oxygen sensors at the minimum. If money isn't an object and you don't want to have to fool with this same issue any time soon then I'd go ahead and replace all four. Then clear the codes and see if that fixes it.

There are resistance ranges that can be measured to determine if the sensors meet specs at room temperature. However, this doesn't guarantee that the sensors are responding to oxygen levels appropriately at operating temperatures. If they are not then your engine will be throwing trouble codes when it reaches its limits of working with the off-calibration sensor. FWIW the LS sensors are three-wire sensors which means that they have a built in heater to get them to operating temperature faster that just waiting for the exhaust gasses to warm them up. This is good for fuel economy but just one more thing to fail.

I don't know if you'll be using a dealer but they will likely hit you for around $80-100 each plus labor. Aftermarkets are less expensive and labor is less expensive. Your choice.