It seems the drive to reduce emissions has ended up with too many O2 sensors and catalytic convertors.
For example, my Lexus RX has 4 oxygen sensors and 2 catalytic convertors. 1 cat has been replaced at 55,000 miles and a sensor replaced twice in last 12 months. Engine management is so sensitive that it throws an engine light and turns off skid control as a precaution. It seems my RX still has the problem, but it is down to a sensor or a catalytic convertor. Either way, for a Toyota vehicle with 65,000 miles that’s not very acceptable.
The death of the Nissan Skyline GT-R was due to emissions, although the new one puts out 500hp with emissions correct.
Still, the days of unleaded fuel used to make me sick, now aircon and cleaner fuels have taken care of this.
Toyota Blog 