AFAIK pretty much all modern cars have 2 x O2 sensors. One before the cat and one in or after it. It allows the ECM to adjust to how well the cat is operating. In our case we have a wideband O2 before the cat (IIRC) and a narrow band in it.
Looks like the graph on the left is your narrowband sensor (AKA: all is cool)
Many late-model imports such as Honda, Toyota, Volkswagen and others use “Air/Fuel” (A/F) sensors rather than conventional oxygen (O2) sensors to monitor the exhaust gases coming out of the engine. What’s the difference? An air/fuel sensor can read a much wider and leaner range of fuel mixtures than a conventional O2 sensor. That’s why they’re also called “wideband” O2 sensors.
Another difference is that A/F sensors don’t produce a voltage signal that suddenly changes on either side of Lambda when the air/fuel goes rich or lean. A conventional O2 sensor will produce either a rich reading (0.8 volts) or a lean reading (0.2 volts) when the fuel mixture changes. An A/F sensor, by comparison, produces a changing current signal that varies in direct proportion to the amount of unburned oxygen in the exhaust.
The front O2 is seeing the direct results of combustion. It sees the firing pulses of the engine as individual spikes. The nice smooth curve on the back end is good.
I do not think those are individual exhaust pulses, I think they are the short-term fuel trim working back and forth around the target value
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