how hard to replace the 02 sensor after the cat.? which is my undertanding that is the last thing i need to replce since i have replaced two of them already.

 

I didn't think this thing was too hard to take out when I modified the tube between the resonator and the cat. However, the two A/F sensors that you replaced upstream and this O2 sensor are two different types of sensors. This one doesn't fail even nearly as much and is not subjected to the same pressures as the A/F sensor, since the precats and cat catch most of the harmful byproducts that can affect the sensors in the long run. Personally, if this one ain't broken don't fix it.

 

Pretty easy, but if the nuts rusted you need to soak them in WD40 for 10-15 minutes before trying to loosen them. Why do you want to replace it? What is the problem you are currently experiencing? Did you check A/F Heater Fuse (25A in fusebox).

 

Here is another look at the sensor.

 

The O2 senser after the cat is easy the only thing is that the plug for it is under the driver's seat. I just replaced my last month.