rear o2 function?

[smslyguy]

I am woundering what the true function of the rear o2 sensor actually are. I do understand that they are montoring the cats, but can they actually add or subtract fuel?

[LM7Tuner]

The purpose of the rear oxygen sensor is to monitor the oxygen content of the exhaust gases leaving the catalytic converter. This gives the emission system a way to monitor the operation and efficiency of the catalytic converters. The rear oxygen sensor checks several things in the post–catalytic converter gases. It measures the amount of oxygen, or peak threshold, in the exhaust gases and follows how fast the amount of oxygen changes. On some vehicles, the rear oxygen sensor is mounted midway in the catalytic converter to measure how efficiently the reduction bed converts NOx by checking the amount of oxygen that is released back into the exhaust flow.

[Ira]

More simply, the rear O2 sensor is not to my knowledge used for adjusting AFR, it is only used to confirm the operation of the CATs.

Ira

[smslyguy]

More simply, the rear O2 sensor is not to my knowledge used for adjusting AFR, it is only used to confirm the operation of the CATs.

Ira

so if you the rear o2 sensor's are reading that the cat's are malfunctioning is there anything the 02 sensor's do besides through as mil light?

[joecar]

Catalyst Monitor Heated Oxygen Sensors
. . .
In addition to catalyst monitoring, the post heated oxygen sensor has a limited role in controlling fuel delivery. If the post HO2S signal indicates a high or low oxygen content for an extended period of time while in a closed loop, the PCM adjusts the fuel delivery slightly in order to compensate.

Do note that this is an abnormal condition.