Diagnosing P0420 Code (need help)

[gadfly87]

I need some help analyzing some data I collected from my 2007 honda fit using my OBDII scan tool and the Torque app.

For some background, my car came up with a P0420 code (Catalyst System Efficiency Below Threshold) after my car experienced a series of massive misfires. To fix the misfiring problem, I replaced all four spark plugs, all four coil packs, did a valve adjustment and replaced the upstream oxygen sensor (the sensor ended up being the main culprit).

The following data was collected over two trips, approximately 30 minutes each. What I'm looking for is a nice consistent wave pattern in the upstream sensor (which was just replaced so I know it's accurate) and a relatively smooth line coming from the downstream sensor.

So after warming up the engine this is what I'm finding at Idle:

https://drive.google.com/file/d/0BwJ...ew?usp=sharing

I get a nice even wave form that averages to about 0.45v on the upstream and an even line at 1.0v on the downstream.

I about the same pattern at higher loads:

https://drive.google.com/file/d/0BwJ...ew?usp=sharing

https://drive.google.com/file/d/0BwJ...ew?usp=sharing

The upstream wave pattern is a little choppy at the higher RPMs because the RPM fluctuates a little bit. After all, this is an actual driving test and not me reving the engine in my driveway.

So the sensor data seems to suggest that I have a well-functioning catalytic converter, right? The upstream sensor is nicely tracking to the variations in fuel trim, the converter is reaching an operating temperature of 600-800 degrees and, as a result, the gases exiting the converter are effectively *converted* to carbon dioxide and carbon monoxide (among other things), right?

Well, the check engine light is telling a different story: P0420.

Then I realized that the converter is only doing its job effectively when it is at operating temperature (a.k.a. when it "lights-off"). Meaning the downstream sensor should draw a similar pattern to the upstream when the converter is cold. The catalytic converter isn't hot enough to break apart the NOx molecules.

So I took the same reading at start up:

https://drive.google.com/file/d/0BwJ...ew?usp=sharing

hmm, well, I could be wrong but, shouldn't I see some more activity in the downstream sensor when the catalyst temperature is below 200 degrees?