How could the code point to a faulty cat, when the O2 signals are normal?

Question

I'm getting code P0420 on an '03 Vibe. The rule of thumb is that this means the catalytic converter is gone. Yet the pre- and post- cat O2 signals appear to indicate that the cat is doing its job.

Unfortunately Toyota/GM have designed the entire exhaust manifold as a single piece, a part whose cost exceeds $1000. I'm not sure that pulling an old cat from a graveyard and splicing it in would be worth it. It may not last and the labor cost would be high.

But given the O2 signals shown above, it's not even clear that changing the cat will get rid of the CEL and the code.

What else could be malfunctioning and causing the P0420 code?

Update

To assist SteveMattews (and other helpful folks) I'm adding a picture showing what the post cat O2 sensor and cable look like. The 90-degree angle that the cable makes at the point it enters the chassis indeed looks suspicious.

Answer 1

I don't think the secondary O2 sensor is reading properly. If the cat were actually shot (a legitimate P0420 code) the bottom graph of secondary O2 should be very similar to the top "primary" O2 aka "Sensor 1".

Keep in mind the cat needs to be fully heated for these graphs to be the most useful. Your pictures look like the Torque cellphone app for a bluetooth OBD2 reader, so I'm assuming you can capture during highway cruise.

In any case, a properly working cat (and downstream O2 sensor) should yield a reduced-amplitude output quite similar to the upstream output. It should rise and fall, and transition roughly the same time.

Your secondary looks pegged rich. Unless the cat was cold, I suspect the O2 is bad. I would not suggest trying to repair the wiring, even if you discover a specific problem.