Oxygen sensors - which one to change?

[RedBeard]

Chilton's says to monitor voltage of HO2 sensors while engine is running... Should swing from .01 to 1.1 rapidly if sensor is OK. 2 of 3 sensors on my X appears to be good.... The other doesn't swing rapidly, sometimes doesn't swing at all for 2 to 10 seconds.

I monitored the voltage(s) with my AutoXray OBD-II scanner (real time monitoring). The sensor in question is identified by the code scanner as Oxygen Sensor 2, bank 1.

They are all identified as
sensor 1, bank 1
sensor 2, bank 1 (sensor in question)
sensor 1, bank 2

Of the three sensors, which one might this be? A tech support email to AutoXray has so far gone unanswered.

Anyone got the skinny on this? Just trying to get the best MPG possible and keep the X in top shape.

-RB

 

[Alec]

I'd say that since 2 of the sensors say sensor 1, and one is sensor 2; that the one in question is the one later down the line by the cats.

 

[RedBeard]

Alec,

Good logic...

I searched some other sites and discovered that "bank 1" is the side of the engine with cylinder 1. Given that, the sensor on bank 1 side, before the cat, would be sensor1-bank1. Bank 2 would be the other sensor before the cat.

So, bank 1, sensor 2 would have to be the one after the cat... it is technically on the side of the truck as cylinder 1... and is the second sensor on that side.

I hope I have this straight... YAHOO!

-RB

 

[RedBeard]

On another message board, someone said that the HO2 sensor after the cat is not supposed to swing rapidly (voltage) and should hover at around .45 volts (that is if the sensor is good, and the cat is doing it's job well).

??

-RB

 

[Alec]

That sounds right. Think about it, the cat messes with all the gases coming out of the motor. Also, I accidentally hooked up my air/fuel gauge to the cat O2 instead of a header O2 when I got it and that's how it acted.

 

[yob_yeknom]

You are correct, it is the sensor behind the cat. RedBeard is also correct. The sensor after the convertor mearly tests the exhaust to make sure the convertor is working properly. If everything is working as it should be, that sensor reading should just barely fluctuate.