can P0446 cause P0420?

Yea... That's the biggest problem with living with a warning light on... You'll never know when/circumstances of when the next warning light comes.

Good news is an aftermarket replacement cat is less than $200 and if you still have your original cat that's failing, the precious metals inside it can be sold for as much as $1800. So you're actually leaving money on the table by not dealing with your P0420 code.

 

No obvious causative link between the two occurs to me.

 

Well, to some extent that's a tautology: P0420 is your notification that $21:$a9 didn't pass, it's not as if they're separate pieces of corroborating evidence.

I'll still stick with my story that I don't see any clear way for your catalyst result to be a consequence of the evap code you mentioned.

I'm not totally clear on Torque's color coding; I think I've guessed what green and red mean, but what does it mean that $3d:$c8 is black?

 

Black means it hasn't run that monitor yet.

I agree the EVAP problem won't cause a P0420.

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Rhodium is up near $700 a gram... And it has 2 grams of Rhodium... It also has a couple grams each of Palladium and platinum which are valuable too... Make sure you don't sell it to someone who is paying thieves to steal them.

 

Decades have gone by since these over-engineered cats were made... These days the ones they make use far less Rhodium. Though you'll likely have more air pollution coming out of your exhaust pipe with them. But then again because your cat is no longer working properly it might be cleaner than what you got. And if you lived in California you wouldn't be allowed to use and aftermarket cat and would have to spend $3-4K on OEM cat.

 

The amount of functional time can vary, depending on the quality of the replacement and the condition of the car it goes into. Some have had several years with no problems while others have a P0420 return after a few months. How much oil an engine burns is a consideration (more oil burned usually = faster cat code).

If I remember correctly, an OE cat has to last (is warranteed for) at least 100 thousand miles (might be up to 150k), while an aftermarket only has to be functional for 25 thousand (maybe 50?).

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