This is what I said above about the Corolla’s 25 year old cat:
Didn’t say it was working like new, just “still working”. The engine continues to pass emissions testing in probably the strictest state for emissions levels in the USA, California. Not just idle emissions. Treadmill emissions. And not just HC emissions levels, NOX and CO levels pass too. And they all pass at both treadmill speeds. That’s the only evidence I can cite the Corolla’s cat is working. But it is pretty good and objective evidence the cat is still doing its job imo.
The HC numbers aren’t quite as high as the 50’s from what I recall, 28 I think is what the last HC test was. 30 and under pass. I don’t know what the current type of emissions test would have resulted when the car was new, b/c CA emissions testing didn’t use the treadmill method then, only idle testing. Next spring the Corolla is due for another treadmill re-test. The drama continues … lol