Diagnosing rear O2's
 

A friend of mine has a 05 GTO and started throwing a Catalytic Efficiency code; PO420.

Anyways, I logged the rear O2's (see attached log and config file if you need it)
And the rear O2's are cycling and doing their thing. My question is, what is normal for rear O2 activity? Should they cycle? How can you tell if they are bad, or something else is wrong?

The car has a Maggie (with standard Magnuson tune), JBA shorties and cats, and 3" all the way back. Borla Catback.

Wires looked good, everything *looked* ok. I think I have the proper PIDs logged, but if not slap me in the head. B1S2, B2S2.

FYI - the chart wasn't setup right when I logged, so use the config or just use the table. Drop the .txt from the config file.

P0420 is a cat code, not a bad o2 sensor code.

Probably wouldn't hurt to just disable the rear O2's, codes, etc. The front ones are the important ones. If the cats go, you'll know by the smell of the exhaust (rich and/or rotten eggs).

I know its a cat code. It means the pcm thinks the cats aren't working right. So my question was how can one confirm or deny this supposition by examining the rear O2 data?

Indeed, I plan on doing that when we go to the Dyno tomorrow, he just wants to make sure nothing else is wrong, and I would like to learn some more about how the PCM interprets rear O2 data to determine cat efficiency.

The pcm basically looks for the signal on the post o2 to have much longer wavelength and lower amplitude than the front sensor because as the exhaust gas passes through the catalytic converter it uses up the majority of the oxygen in the exhaust so if the cat is working properly the rear o2 should measure less oxygen than the front o2

yeah im not sure of the exact pattern the pcm looks for to throw a cat code...i could only assume it would be looking for less switching then the fronts...other then that im not sure of the pattern.

If you plot the rear o2's you should look for the signal to be almost a flat line. If the o2's are toggling like the fronts do, then you most likely have some converter issues. Generally you should should see a leaner reading after the cat due to the converter releasing oxygen, but not always the case. I have seen some hold a line at 400mv and some at 750mv, but what you are looking for while plotting is a flat line. And if you do have a bad cat and car is under the 8yr/80,000 miles emissions warranty, then take it to a dealer and get it replaced.

I wonder if they can deny warranty on an emissions part since he's got a blower...

Thanks for the info guys. Helps to understand the logic behind it.

Yeah, no way this will be under warranty, these are JBA cats, the entire exhaust is aftermarket.

Some dealerships will warranty converters on vehicles with blowers, just depends on the dealer. Though they would have to be factory converters. I just got a new bulletin today regarding converter replacement on some 2000-2002 camaro and firebird with the ls1. Depending on the vin breakpoint, converters are covered to 10yrs/120,000 miles.

Service Bulletin
 

Does anyone have this service bulletin? I am at 95,000 and the dealer says all cat warranties are 80,000 - he never heard of 120,000.

Thanks,
Bill