我还是建议你找个手册。我的Camry手册描述的过程并不很简单

这东西不光是震荡范围，还有波形。输出到ECM的信号是另外的。需要在不同的probes之间测量。最好找到本田的维修手册或者Haynes手册。需要比较前后sensor 的波形和输出。

我仔细看了看我的Camry手册，现学现卖。

O2 sensor 回路故障另外有码（P130,133,135,136 and 141）。P420 专指催化系统效率未达到要求。如果你仅仅读到P420而没有其它码，好像确实要怀疑催化剂失效。但你的现象仅仅在雨天出现，我觉得还是什么地方的电路问题。而且你说后面的sensor波动速度慢，根据下面的原文，如果催化剂坏了，前后波动速度应该一样。

另外一个怀疑点是空气进口A/F sensor。



摘录原文供你参考。

The ECM compares the waveform of the heated oxygen sensor located before the catalyst with the waveform
of the heated oxygen sensor located behind the catalyst to determine whether or not catalyst performance
has deteriorated.
Air–fuel ratio feedback compensation keeps the waveform of the heated oxygen sensor before the catalyst
repeatedly changing back and forth from rich to lean.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor behind the catalyst switches
back and forth between rich and lean much more slowly than the waveform of the heated oxygen sensor
before the catalyst.
But when both waveforms change at a similar rate, it indicates that catalyst performance has deteriorated.

(a) Connect the TOYOTA hand–held tester to the DLC3, or connect the probe of the oscilloscope between
terminals OX1, OX2 and E1 of the ECM connector.
(b) Start engine and warm it up with all accessories switched OFF until water temp. is stable.
(c) Race the engine at 2,500 ~ 3,000 rpm for about 3 min.
(d) After confirming that the waveforms of the heated oxygen sensor (bank 1 sensor 1 (OX1)), oscillate
around 0.5 V during feedback to the ECM, check the waveform of the heated oxygen sensor (bank
1 sensor 2 (OX2)).

If there is a malfunction in the system, the waveform of the
heated oxygen sensor (bank 1 sensor 2 (OX2)) is almost
the same as that of the heated oxygen sensor (bank 1
sensor 1 (OX1)) on the left.
There are some cases where, even though a malfunction
exists, the MIL may either light up or not light up.