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NICKG is right on the money ( he ought to be, he does it or a living, right?).
If you don't have a OBD scan tool with real - time engine, and sensor monitoring, everything is little better than a guess. With a scan tool you can look at all four O2 sensors, and monitor the activity. Post-cat sensors will have an even, slow voltage stream, but they should show fluctuations in voltage. A pre-cat sensor should react quickly, and be all over the place voltage wise once the car warms up and enters closed loop, unless you have a perfect engine that has all cyliders perfectly balanced (I've never seen one).
OBD2 warm up, and actual temperature warm up are two totally different things. Part of the OBD2 protocol, is that the o2 sensor has to be warm, measuring the exhaust stream, and in closed loop in a preset time from the first time that engine fires and runs. This is why we have heated O2 sensors.
I don't think cats will go bad for the lifetime of a car IF it's kept in tune, and you run good fuel in it. Sulphur, and constant exposure to trash gas is usually what gets them. At a salvage yard my friend owns they have a yard truck that ONLY gets gas from incoming totals. These totaled cars may sit in the insurance pool lots for up to a year. We call that "Swamp Gas" The yard truck will run on it, but not well, but it hasn't killed a cat yet in 3 or 4 years, so they are more robust than people think.
NICKG, flat time is killing these techs, and turning them into parts changers, but there are still a few good ones around. Customers scream bloody murder when they get charged two hours for diagnostics.
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