2000 S80 T6. P0036 and 136 codes (bank 1, sensor 2). Replaced both downstream O2 sensors with Bosch units. Still throws codes. Disconnected battery for 10 minutes, still throws codes. Idle is rough. Hesitates on acceleration. Cleaned MAF sensor. It has aftermarket plugs and a few aftermarket coils. No evident vacuum leaks. I have the voltage measurements from the scanner. They are identical on both banks, but I am not sure how to interpret them. The rich-ln and ln-rich thresholds are both 0.605 V. The min V for cycle show max 0.595, the min is 0 and the measured is 0.190. The max V for cycle shows max 1.075, min 0.615 and measured 0.720. Any suggestions? Thanks for the help!

 

Update. I replaced the MAF sensor and removed and cleaned the throttle body. The idle is now smooth and acceleration is normal now. After doing this, the P0036 went away, but the P0136 code remains.

 

I spoke with my mechanic today. He thinks that given the voltages, that the upstream sensors are bad. He says that info from the ECM goes through the upstream ones to the downstream ones and if they are defective, it will throw the code for the downstream sensor (0136).