My 06 Prius gave me check engine light. OBDII says it's P0420. catalytic converter below efficiency. My OBD show that: oxygen bank1 sensor 1 voltage is constant is 0.66 oxygen bank 2 sensor 2 voltage fluctuate I am suspicious that the bank1 sensor 1 is bad. My theory is that the voltage should be at least 3 volts and should fluctuate instead of being constant??? if it's constant, then the sensor must be bad. Can anyone confirm? My 06 Prius has fuel air ratio sensor instead of oxygen sensor. I am guessing that's what I need to buy and replace?
What did you use to check the live data? If oxygen sensor 1 would actually stay at 0.66V it would have other codes as well. If oxygen sensor 2 switches (pretty fast) between rich and lean it can only be the catalytic converter.
I'm surprised you have not got codes relating to a/f sensor (B1S1) and the rear o2 sensor ( B1S2) given the voltages you observed on those sensors. A P0420 is catalytic converter below efficiency, and does not necessarily mean the cat is bad. You are correct, B1S1 should show a fluctuating voltage and B1S2 should be a constant voltage. Are you sure you got the reading the right way around?
I found this useful technical documentation. It said voltage should be 3 volts indeed. I use bafx obd II tool to get live voltage data. I am surprised that it did not show sensor 1 malfunction code. Only p0420 code. It should have, as the voltage is only 0.66 "constantly. Anyway, I will try and replace a new air fuel ratio sensor and see if p0420 goes away
Sounds more like the problem with your diagnostic tool/program. Best software to diagnose (and do maintenance for a Prius is Techstream. Mini-VCI is cheap and good way to get it. But just trying some other universal code reader might get the correct voltage information from oxygen sensor 1. Or of cource you can just measure the voltage from the connector before unnecessary replacing the sensor.
