Oxygen sensor circuit malfunction?

Hello, this code is for the front Air Fuel Ratio sensor, it's not really an oxygen sensor but it takes the place of the front oxygen sensor. This is for Sensor 1 Bank 2 which is on the left side exhaust manifold (driver side). I'll post a diagram of the connector, but most likely what happen is the heater circuit inside the AF sensor has failed and is now and open circuit, hence the circuit Low code. So, you'll have to unplug the sensor and measure the resistance of 2 of the 4 pins going to the AF sensor, with a multimeter set on the resistance (Ohms) setting. It's a low resistance spec. Will post that as well in a minute.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

These are the wiring diagrams for the B2 front Air Fuel Ratio sensor, do not touch any bright Orange High voltage wires, if you are unsure about what you're doing, have a shop do it. These high voltage systems can be 400 volts or more. The AF sensor works on the 12volts side of the system, and you will only be unplugging the one sensor and checking the resistance across 2 of the pins in the connector that goes to the sensor. Most likely you are not going to read any resistance because the heater inside has failed, if it was a voltage feed to the sensor there would be a code for Bank 1 as well. So, I think you'll find you just need to replace the one sensor. It's a very simple test, key Off, engine Off. Unplug it and check with the meter leads on pins 1 and 2. those are the heaters for the sensor. If it has failed dent buy a cheap aftermarket sensor, because it will just fail prematurely or not work at all. Check the sensor in the morning when the exhaust has cooled off. The reading is supposed to be taken at 68 degrees f, so ambient temperature.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

You're welcome, just be very careful. The high voltage 3phase wires are very thick orange colored wires for the electric motor. Avoid touching any of that section.

Okay, are you all set with how to test the AF sensor heater? If the heater is open circuit inside the sensor, the sensor will not function at all. These are nothing like conventional Oxygen sensors, the heaters in these get to extremely high temperatures for proper operation. They still send lean or rich exhaust data to the ECM, but they do it by current flow and not a voltage level. They are also very expensive. I recently purchased one for a 2007 Pathfinder I'm working on and the OEM was $307, but the customer could not afford that price, so I did find a Denso sensor on Rockauto com for around $100 which is an okay brand. So, if you find the sensor needs to be replaced check there.

Here is the link for your vehicle straight to the AF sensors, they call it an oxygen sensor here as well, but you're looking for the upstream sensor so Sensor 1 Bank 2.

https://www.rockauto.com/en/catalog/toyota,2006,highlander,3.3l+v6+electric/gas,1431836,exhaust+&+emission,oxygen+(o2)+sensor,5132

I see some Denso, Delphi and Bosch from about $105 to $185 range
The Bank 2 sensor is in the front of this vehicle, it's under the upper heat shield on the exhaust manifold. So, these ones are easier to get to, if you get the exhaust hot, they come out easier most of the time, just wear gloves. Here is the OEM part number as well.

Okay great, guess I was a little too slow on that one, sorry about that.