Sensor code woes
 

I may not have enough details for anyone to offer help here, but I have to try.

I have a 2006 Camry LE (4 cyl.) which got a new (factory) catalytic converter in early September, the one mounted on the front of the engine (the car has 94,000 miles). I replaced it because it had an after-market on it when I bought it that had no shields. I decided to ante up and get a new cat so it could be properly covered. In about a month the check engine light came on. My mechanic said it was an 02 sensor. He changed the downstream one that has connections running up into the car under the seat. The light came back on. He changed the other downstream sensor. The light came back on. Getting a 0 volts reading on the last sensor he put in, he put another one in. The light came back on. Because I was away for a week, further work was delayed until today. The diagnostic today wasn't conclusive; I think he said the codes were 136 and pending 137. He thought it looked like the air/fuel sensor was the culprit. So that was changed. The light came back on tonight.

He said this morning before that sensor was replaced that it could be the computer. Has anyone had this kind of thing happen who might think it's the computer? What else could it be? I know there are other variables (bad connections and contamination, for example), but he checked what could be seen. Is it time to take it to a Toyota dealer?

Any exhaust leaks?

Was the EFI checked?

Did the mechanic use Toyota or Denso brand parts?

I don't know about the first two. They used Denso.

Denso is good!