One problem related to o2 sensor has been reported for the 2001 Toyota Avalon. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2001 Toyota Avalon based on all problems reported for the 2001 Avalon.
I have replaced O2 sensors twice to get rid of the check engine light for codes that have popped you p1135 & p1155. Took car to two different mechanics and Toyota dealership and no one could figure out why the light is still on. All sensors have been replaced with denso parts. This seems like a recall if not even the Toyota dealer could fix the problem. There are many people having the same issue with Toyota's. I need my car to pass a smog and it could not because of this issue. Car only has 62,000 miles and runs great.