[duffyatkinson]

Originally Posted by chinaloy

i changed my front sensors a year and a half ago, approx 9000 miles. I have just changed my bank 2 sensor 2. I have not changed the other one yet, because the weather stinks.
i do not think there is a correlation between the fronts and the rears.

BTW, i have about 135,000 miles on the truck.

I used oem sensors for the front and am using Bosch universal sensors in the rear.

so far so good

There is a SIGNIFICANT relationship between the upstream and downstream sensor units. The upstream (air/fuel mixture) sensor gives direct feedback to the ECU to enable an efficient fuel/air mixture given engine circumstances. The downstream (emission oxygen) sensor helps the ECU monitor the effectiveness of the catalysts system's emission control functions. The ECU has to monitor not only the sensor readings but also the heating up ("lighting off") cycles of the sensors and catalyst components as well, i.e. the ECU ignores the downstream readings until the cats reach effective operating temp. (The sensors receive voltage to get them up to operating temp quickly, just a few seconds). The ECU uses the data returns from BOTH packages to make sure that the fuel/air mixture stays around the stoichiometry (for gasoline - 14.7:1), operating the catalyst most effectively.

And dump the Bosch components. They'll cause you problems down the road. Stick with NTK or Denso. The Toyota ECU is really picky about you trying to use "universal" components here...