The OS is mounted right in front of Cat. How can it detect bad Cat if car is designed to have only one OS?

 

Do an E-check. Do u even have to do an E-check in GA? If not, Test-pipe that monkey, lol.

 

what year is your car?

and btw cats don't go bad on their own, they only go if your car isn't running right.. IE too rich and is getting it wet with unburned gas. the o2 sensor montiors whats coming out of the engine, and then tells the ecu which then tries to even everything back out to a 12:1 ratio i believe.

 

91 EX. Codes call for, I believe, bad Oxygen Sensor. I just replaced it 2 years ago and Cat 3 years ago. How can Oxygen Sensor know if Cat is bad other than just replace part one by one. Autozone doesn't do E-check for 91. I did wire jump check a while back.

 

o2 sensors do go bad... if its a o2 sensor code then replace it.

 

What DTCodes did you get when you jumped the SCS? I just noticed that you said that you "beleived that they were Oxygen Sensor" codes. It could be something else causing the code.

 

it doesnt detect a bad cat, it provides feedback for the ECU under closed loop conditions (which targets 14.7:1 A/F ratio).

Thats why cars meeting newer emissions standards have the second sensor after the cat.

 

I checked the code by mean of wire jumping (actually I used paper clip) a while back and don't remember the code. It could be 10 or something. I just remember it's about O2 sensor. It's could outside I will check it again in the next couple day when it's warm.