[QUOTE=selbox]from renntech.org
P1128 Oxygen Sensing Adaptation Area 2 (Cylinders 1 - 3) - Rich Threshold
whatever that means
QUOTE]
It means the fuel/air mixture has passed the rich threshold on the cylinder 1-3 bank. Too much fuel is put in the mix (rich) so some of it does not ignite in combustion. The fuel that does not ignite goes down the cats and the 02 sensor detects fuel beyond it's pre-set threshold. The computer tries to adjust the mixture, but if it cannot get it down below the threshold it assumes there's a problem and you get the code. There is a threshold set because even in perfect mixture conditions there is a little fuel that does not ignite. It's usually the 02 sensor going bad and creating bad readings.
This can be dangerous because too much left over fuel in the really hot cats can give you a cat fire.
Hope that helps.
