how do cats go bad causing need for replacement? are the stock cats prone to this problem? do all cats have a "lifespan"?

 

I've had both of mine replaced under CPO. I don't know what came loose internally but it sounded like hell when it did. BTW, my car is an '03 with 61K miles. Both were replaced in the last 10K miles.

 

One of my ctas was replaced recently and the other need to be replace soon. 86,000km
Porsche has a 8 year warranty on Cats.

 

they wear out. The active layer of catalytic metal is just atoms thick and while these atoms are pretty tightly bound to each other and their base metal they can break loose over time. As they do the efficiency of the converter to store oxygen for post processing of exhaust gases is diminished.

When it decreases to a certain threshold the engine controller determines this by the signal being generated by the post-converter O2 sensor. It starts to generate a signal that it is in some way too much like the signal being generrated by the #1 or pre-converter O2 sensor.

The signal from the #1 sensor varies because the engine controller constantly alternates between supplying the engine with a rich then lean mixture on the order of just a fraction of a percent richer or leaner than ideal (approx. 14.72:1). The signal from a #2 sensor that is after a properly functioning converter should signal an absence of oxygen with the assumption the oxygen was used by the converter.

When the signal indicates oxygen is present above a certain level this is because the converter can't store the oxygen in times of excess oxygen in the exhaust gases for use when the exhaust gas is low in oxygen content.

Are you sure converters are bad? How? A bad or going bad O2 sensor can fool you. I've had to replace several O2 sensors and yet not one converter, but....

....I've got over 207,000 miles on my engine's converters and one still works just fine. The other one doesn't work so good. The engine controller generates a P0430 error code almost every day now. The converter is just worn out.

Sincerely,

Macster.

 

Macster: Thanks for the explanation. I have wondered just exactly this--I knew there were O2 sensors, but really did not know the mechanism. It sounds like I will get an error if my cats quit working.