Oxygen Sensor - Replacing

[Avensis Avenger]

Dear friends,

I am suffering P0031 - Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1). I would like to replace the sensor myself rather than pay Toyota £340. My Avensis is a 2005 2.0 petrol VVTi (1AZ FSE).

I have attached a picture of my engine. I have circled in yellow where I think the o2 sensors are, although cannot be sure. I have also circled where two of them go into the engine. Please take a look.

I have a few questions which I would greatly appreciate any advice on:

1. Have I identified the o2 sensors (or parts of them) correctly? Am I right in saying that we have Bank 2 on the left hand side as we look at the picture and Bank 1 on the right? B2 S1 being the innermost (grey) one of the left and B1 S1 being the innermost (grey) one on the right? This seems to make some sense given the diagram here: http://www.toyotaownersclub.com/forums/topic/112018-o2-sensor-heater-malfunction/ although the B1S1 and B2 S2 are not marked on that diagram.

2. Resistance. Following some advice on the forum I tested the resistance across the top two terminals of each o2 sensor with a multimeter/ohmmeter. All except the one that I suspect is B1 S1 read around 10-15 Ohms a little while after a run. The ohmmeter reads one (as the ohmmeter does when not connected to anything). This would suggest an error in the sensor in question. However, the engine warning light seems to have gone away since I jiggled, removed and replaced the o2 wire from the socket to test resistance. The resistance still reads zero. Why has the warning light not come back on in the resistance reading is zero?

3. What part number is Bank 1 Sensor 1, or what name does this have? I can see many online for instance at Euro Car Parts, with differing descriptions such as "right hand upper", "left" and "left hand lower" but I am not 100% sure what this means and don't want to buy one from a guess. I would guess B1 S1 is "upper right" owing to where the sensor enters the engine. Can anyone confirm?

4. Replacement. How complex a job is replacement? As far as I can see this would be relatively simple - (unclip the grey socket, unscrew the sensor engine-side and replace). Is there anything further I need to be aware of as Toyota quote 1 1/2 hours!!

4. The Manual. I have the service manual on CD but for the life of me cannot find where information on oxygen sensors including part numbers. I find the manual very difficult to negotiate. Can anyone direct me to the relevant section/s please?

Any advice would be greatly appreciated.

Kind regards

Avenger