MIL and O2 Sensor Issue

[zoidberg444]

The typical design I see on Toyota's at least is the bank 1 sensor before the catalytic converter is an AFR sensor and the bank 2 sensor after the cat is a standard zirconia oxygen sensor. Toyota have been using that method on some of their other vehicles since the early 2000's but it looks like the Yaris only just got that treatment.

Another good site with similar capabilities is www.partsouq.com which has the annotated parts diagrams along with the part numbers and it looks like not only does your NSP90 model have a 1NR-FE engine according to the parts numbers it also looks like the bank 1 sensor is an AFR sensor and the rear sensor is a standard O2.

AFR sensors are kind of weird. Instead of oscillating between 0-1V the Toyota ones in a normal functioning engine will show around 3.3V although the voltage doesn't actually exist the ECU generates that value for the scan tool but they are actually creating a tiny amount of current that the ECU measures but that would be virtually impossible to measure externally. At least that's my understanding.