You should be changing B1 S1 (Air Flow Ratio Sensor) for P0138.

See this thread.
Here is another.

For some reason this screws up everyone thinking it is B1 S2.

 

Thanks for the links to those threads DL175! After reading them, I assume you mean to next replace the Bank 1 Sensor 1 (Air Flow Sensor)? ( I already replaced Sensor 2). I'll try that fix this week and report back.

Ian

 

Fixed!

Reporting back. I replaced the Air-Fuel Sensor (bank 1, sensor 1) and reset the error codes. I've driven a couple hundred miles and the lights have not come back on. Thanks for the assistance!

One note, the old sensor was very difficult to remove and the new one difficult to install. I've since learned I should have re-tapped the threads with an oxygen sensor thread chaser. Oh well, it's probably now a permanent install.

 

I have 2006 Rav4 4cyl. This car burns oil and in humidity the air to fuel mixture is Incorrect and O2 upstream codes come on. When it stop raining, everything is OK. I took out the O2 sensor and cleaned it. But my engineering background persuades me in a direction of improper calibration for humid environment. When you add oil to combustion and decrease significantly O2, you need higher degree or order of calibration.

 

I have 2006 Rav4 4cyl. This car burns oil and in humidity the air to fuel mixture is Incorrect and O2 upstream codes come on. When it stop raining, everything is OK. I took out the O2 sensor and cleaned it. But my engineering background persuades me in a direction of improper calibration for humid environment. When you add oil to combustion and decrease significantly O2, you need higher degree or order of calibration.