p0420

[crankor]

This code came back after about 3000 ish miles of driving. I find it odd that it always seems to be the bank 2 side whenever people get this code. I havent dug into it much but for now I suspect maybe a loose exhaust connection due to the temperature drops recently. Cats are new although not oem, the b2 upstream sensor was replaced but I forget if the downstream one was. The only difference I noticed so far from the live data between the sensors is the suspected one does very briefly sometimes dip into a negative number. Seems overall there aren't many of any topics of their fix. Ah well. I imagine i wouldn't see much difference in the readings at just idle?

[VStar650CL]

The fronts are wideband and not HO2S, so problems with those are generally easier to sort out from scanner data. However, there's no way any HO2S sensor should go negative voltage, even with the sensor flatlined before warmup. If there was a pinhole leak near the sensor then the behavior would be consistent and not erratic, so I'd say that sounds like either a bad sensor or resistance in the signal wire.