02 Aurora PO420 code

ksierens · #1 10-04-2011, 02:10 PM

So I had a PO410 code for a while. Eventually replaced the pump and the passenger side value (both bad) and I thought "Well finally the CES light will stay off" So I was out today and of course, it pops back on with a PO420 code. Seems to be a very common code for many cars and looks like the cat is bad. Anyone else have experience with this?

Tech II · #2 10-04-2011, 04:02 PM

Basically, you look at the plot of the pre and post O2 sensors.....if they mirror each other , the cat is bad.....

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