Oxygen Sensor Questions

[MisterRoy]

From what I've been reading, upstream sensor voltage bounces around and downstream voltage should stay consistent. I am monitoring my 02 sensors via Forscan. It seems that the upstream sensors are working as expected. The downstream, well, I have one that I've observed around.74 - .85 volts consistently. The second is bouncing around like the upstream sometimes, and others it may be consistent, like the other. The car temp was 205 degrees according to the coolant sensor the last time I witnessed this activity.

If a downstream sensor is bouncing around, is that indicative of a bad sensor or a malfunctioning cat? If I am not understanding something, educate me.

Thanks!

MisterRoy

 

[joegr]

I'm pretty sure they are supposed to move around a little, just not as much as the front ones (unless the cat is bad).

 

[MisterRoy]

I'm pretty sure they are supposed to move around a little, just not as much as the front ones (unless the cat is bad).

A bad cat would have other symptoms and throw a CEL right?

 

[milehighmikey]

Right, P0420 most likely.

 

[BILLBOATS]

If your catalitic was bad to the point of making performance poor, such as slow , say 15 sec 0-60 then you would experience a bad catalitic . Those numbers to me don't warrant buying another replacement. Also you gas mpg would decrease. A bad cat plugs up and suffocates the breathing of the engine.

 

[hrmwrm]

there are 2 ways a cat goes bad. it just stops functioning, or it is plugging off. a code for a non functioning cat will come up. a plugging off cat will hurt performance.
if it sets a code for cat not working, it could also be the o2 sensor going bad.

as long as there are no symptoms of anything, like no code and no performance problems, it isn't something to worry about.

 

[MisterRoy]

Thanks for all the replies. I am learning new things as I troubleshoot a hard start condition when warm. The cats seem fine. Everything seems fine sans a fuel injector or something.

Thanks!