After cat O2 sensor ?

[LTond56]

I know the PCM does not use after cat O2 sensor data to regulate fuel/air but if the heater circuit fails (SES P0141) does that cause it to run in open-loop?

[fdryer]

Simply, no, because of the same correct assumption about the front O2 sensor; the front sensor is used (when its at operating temperature) to regulate the air/fuel mixture in closed loop mode. If this sensor fails then the EFI system will run in open loop mode. The rear sensor is monitoring the catcon output to rat you out to the emission inspector if the catcon goes.

[Low Saturn]

The heated oxygen sensor (HO2S) is mounted behind the catalytic converter. This sensor is used to determine the oxygen storage capability of the catalytic converter. Oxygen storage capability is used as a measure of converter condition, and its ability to perform its function. Due to the location of the rear HO2S, it requires additional heat to operate properly. This sensor incorporates a heater (12 ohms), which is controlled ON or OFF by the powertrain control module (PCM). The PCM diagnoses the heater and its related wiring by monitoring electrical current. A DTC P0141 will set if the current range does not fall within the calibrated limits.

Conditions for Setting the DTC:

DTC P0141 will set if the following conditions exist for longer than 50 seconds when the catalyst temperature is less than 775°C (1,472°F) and:

-The current feedback is less than 0.5 amps OR
-The current feedback is greater than 2.4 amps.

Diagnostic Aids:

Normal scan tool readings in closed loop will show the oxygen sensor voltage varying between 10-999 mV.

[LTond56]

Thanks for the detailed response. Not sure yet what the problem is but the P0141 eventually comes back. If the car is driven right after it is started it never shows up. Sit idling too long from a cold start and it always comes back. Connector and wiring back to sensor are visibly good but connector forward disappears in a black hole above the starter. Wish I had a lift! My condo complex does not appreciate cars on jack-stands either. The heater circuit DTC P0141 is the only one that shows up so can I assume the rest of the sensor and the cat are fine?