Check Engine Lights

I have a 2003 Toyota Sienna mini van and has done 86,000kms. Two weeks ago check engine lights came on. I took it to a mechanic who checked it out on his computer and found that O2 sensor at Bank 1 Sensor 2 is bad. So we changed it with a genuine Toyota O2 sensor. The lights went off after the reset. Immediately thereafter I got the emission test done. It failed. Mechanic said it will take time for the onboard computer to reset and will take time so drive for a couple days and come back for a retest. Lo and behold the lights came back the next day. I took it to the mechanic again. He checked the wiring…the wiring to and from all the sensors are OK. He suspected it could be due to the spark plugs so we changed that and reset the “CEL”. The lights came back again the next day. Mechanic suggested I take it to Toyota dealer to check it on their computer…and I did. They told me it is the same sensor that is bad. Is it possible that the sensor could have a (manufacturing) defect? if so does Toyota warranty their part? How do I prove to Toyota that the part could have a manufacturing defect. Or could it be something else? Catalytic converter for instance? How do I get rid of this “CEL” from the panel once for all. This is the second time I have replaced this O2 sensor. The first time it was changed within one year (in 2004), however since it was under warranty then, Toyota replaced it for free. But now the replacement costs almost $450.00 including part and labour. I also want to know if this is a generic problem on Toyota vehicles? I have a friend who bought a new Camry last year. He replaced 2 sensors recently but since the vehicle is still under warranty they did it for free. I had a 1997 Camry that had done 154,000 when I bought. I sold it three years later after adding 100,000 on it…no problem with anything. Toyota’s newer vehicles might have this problem with the O2 sensors…I could be wrong…I hope I am wrong. I hope some one at Toyota is listening. Thank you.

I would hope that the $450 included more than just the part and labor to replace it. Someone else may have a better grasp of a fair cost on this item.

How about posting the actural error code (like P1234).

I suspect there is another mechanical problem causing the errors, like maybe a leaking injector. OK I could be way off.

The front sensor is $206 MSRP, which is very high to me. Rear sensor is $100 or so. I think the issue is something other than the sensor, also, so posting the code would be helpful…