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Old 12-31-2015, 11:34 PM   #5
jb92563
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Join Date: Apr 2012
Location: Riverside, CA
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The post cat sensors Voltage are supposed to show a low amplitude wave close to a straight line.
The blue line seems to indicate a sine wave similar to what the precat sensors would be reading meaning that the cat is not working.

Its also a little erratic so perhaps you have not gotten the cat hot enough.

I'd try a few more minutes of vigorous driving or highway to make sure the cats are hot enough to be working properly.

If there is no improvement, it means that the cat is no longer functioning efficiently.

I have just dealt with a similar issue but had the Cat 420/430 code on my 2001 S with 75k miles.

If you resolve the other codes first and the problem persists it may need the cat replaced.

Normally a cat will last for the life of the car, but they can fail by becoming plugged/fouled with oil/carbon deposits, ceramic element can be broken up or the cement holding the element in place can fail/leak.

Replacing the cat with a used one from ebay (~$250) solved the issue in my case but I was not getting the other codes you are having.

My defective cat had its element come loose inside the cat and presumably allowing enough exhaust gas to bypass the element that it produced the CEL codes.
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Last edited by jb92563; 12-31-2015 at 11:41 PM.
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