Diagnosing rear O2's
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From: Castle Rock, CO
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.
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.
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).
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From: Castle Rock, CO
Originally Posted by foff667
P0420 is a cat code, not a bad o2 sensor code.
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From: Castle Rock, CO
Originally Posted by SSpdDmon
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).
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.
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Launching!
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From: Hebron, Oh
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.
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From: Castle Rock, CO
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.
Yeah, no way this will be under warranty, these are JBA cats, the entire exhaust is aftermarket.
Launching!
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From: Hebron, Oh
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.
Staging Lane
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From: San Antonio
Service Bulletin
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.
Thanks,
Bill
