Aftermaket exhaust, PO420 code?

[AlaxyGalaxy]

Alright, so I borrowed a bluetooth OBD-II dongle from a coworker and managed to watch the two O2 sensors in real time.

Since I use a free version of an app, I can't log what I graph, but here is the gist of it:

B1S1 varies from 0 to 0.9 (volts, I'm assuming) continuously, and is affected by throttle input.

-When the cat is up to temperature, at idle and very little throttle, B1S2 is stable at around 0.8; that seems a little high to me.
-On compression or during a shift, B1S2 drops to zero, mimicking B1S1.
-At middle throttle, B1S2 mimicks B1S1 almost exactly
-I have not tried WOT.

Sometimes, with very little throttle, B1S2 will jerk up or down, then get back to being stable.

This behaviour seems quite odd to me: I was assuming that at temperature, B1S2 was supposed to stay stable at around 0.5-0.6V and not vary much at all. Mine is stable (albeit a tad higher), but only at low throttle input.

I have to admit I have absolutely no reference point. I think I'll plug the dongle in the Sienna and monitor one bank of sensors, just to see what a system that doesn't throw a CEL is supposed to look like.

[B.B._07]

Originally Posted by AlaxyGalaxy

Alright, so I borrowed a bluetooth OBD-II dongle from a coworker and managed to watch the two O2 sensors in real time.

Since I use a free version of an app, I can't log what I graph, but here is the gist of it:

B1S1 varies from 0 to 0.9 (volts, I'm assuming) continuously, and is affected by throttle input.

-When the cat is up to temperature, at idle and very little throttle, B1S2 is stable at around 0.8; that seems a little high to me.
-On compression or during a shift, B1S2 drops to zero, mimicking B1S1.
-At middle throttle, B1S2 mimicks B1S1 almost exactly
-I have not tried WOT.

Sometimes, with very little throttle, B1S2 will jerk up or down, then get back to being stable.

This behaviour seems quite odd to me: I was assuming that at temperature, B1S2 was supposed to stay stable at around 0.5-0.6V and not vary much at all. Mine is stable (albeit a tad higher), but only at low throttle input.

I have to admit I have absolutely no reference point. I think I'll plug the dongle in the Sienna and monitor one bank of sensors, just to see what a system that doesn't throw a CEL is supposed to look like.

It looks like your cat is operating as it should at idle and minimal throttle but is not doing it's job at middle throttle. Since most of time when you're driving you're using more than minimal throttle the ecu is recognizing the cat is not working right and hence the P0420 code.

O2 sensors produce output between 0.1V and 0.9V, with the presence of oxygen inhibiting or lowering the output voltage. A cat is used as a big hot (emissions fighting) furnace to burn off all the unburnt hydrocarbons exiting the engine and in the process using up the available oxygen to make C02 and H20. In a properly working system the B1S1 02 sensor will fluctuate up and down like a sine wave as the engine constantly switches between running too lean and too rich, and the B1S2 02 sensor will output a more stable mid to high voltage as the cat is using up most of the oxygen in the exhaust. So my suggestion would be go back to your stock cat and get that Walker mid pipe.

There's a bunch of good videos on youtube explaining the P0420 code and cat inefficiency.

https://www.youtube.com/watch?v=vKLFO8MF7SY

https://www.youtube.com/watch?v=vKLFO8MF7SY