I have tried to link my scanner (Foxwell NT204) to Romraider but it does not have the ability to output/export data.
I have the freeze frame data from when the ECU threw P0420, see attached, which shows STFT3 & LTFT3 trimming big time. From my limited understanding that will be the trim on injectors 3 & 4? What would that indicate?
In regard to the freeze-frame data, other than the ST and LT #3 fuel trims, most of the other parameters appear to be fairly normal. (There's a few I'm not familiar with.)
The #3 trims are based on feedback from the rear O2 sensor. The "-100%" is very odd, but that might be the way the Foxwell scanner is interpreting the data (which could be zeros in both cases).
In my 07 logs (and others posted here), the LT #3 is zero, and the ST #3 usually varies while driving, roughly plus and minus 2%. At fully warmed up idle, with the rear O2 voltage above 0.6 V, it's 0.3%. We're not sure how the #3 trims interact with the #1 ST and LT trims that are based on the A/F Sensor, but there is evidence that the rear O2 voltage influences the overall trim. (The #3 trims, as with the #1s, are not cylinder specific.)
If the Foxwell can, monitor the two #3 trims while the engine is idling to see if they're holding at the -100% level, and then again while driving steadily; in other words, not at a particular "freeze" moment in time. Also, look at the rear O2 voltage and the STFT#3 while the warmed-up engine is idling.
Turning to the code itself, the detecting criteria used by the on-board diagnostics is based on a statistical analysis of the high/low changes in the signals from the pre-cat A/F Sensor and the rear O2 sensor over time. A very simplified explanation might be: If the number of changes in the signal from the rear O2 is significantly greater (statistically) than the changes in the signal from the A/F Sensor, then the OBD interprets that as a fault in the cat converter.
I've attached the Detecting Criteria for the P0420 code which provides more detail on the statistical foundation. Because it's a time frame analysis, the "snapshot" that the freeze-frame data provides is often not of use unless there's a very obvious anomaly. Note that the test of the cat converter is performed only once during a drive cycle, and the code is set only if the fault is detected in two consecutive drive cycles.
It is because of the "over time" and statistical analysis aspects, and the fact that cat performance can be influenced by various engine operating conditions, that logs of multiple parameters running over time under different driving conditions can be helpful in trying to distinguish between a truly faulty cat, and a code that might be caused by other factors. In many of the posts here, cardoc lists the parameters to be examined.