O2 wiring diagram

the back manifold ( closest to the fire wall) is bank l
there are not 2 x O2 sensors up stream
they are heated oxygen sensors (HO2S) and are in the manifold or exhaust pipe before the cat converter
The 2 x O2 sensors are after the cat converter in the exhaust pipe
so bank 1 sensor 1 is a HO2S sensor
there is a difference in the sensors as the HO2S report exhaust gas conditions to the ECM for fuel /air adjustments , have 4 wires and are heated to read the gas correctly
the after cat converter sensors ar O2 sensors and report on the cat converter action to further adjust the air /fuel mix in the ECM

It's the only sensor or part in the exhaust that has a wire to it. It is often found right on the exhaust manifold, or in the exhaust pipe just beyond the exhaust manifold. It is threaded into the exhaust, and was installed with anti-seize compound on the threads, making it easy to take out.

Some vehicles have this oxygen sensor for fine tuning the fuel metering, and a second O2 sensor in the exhaust after the catalytic converter, there solely for monitoring the efficiency of the converter.

Hi John:
According woth the repair manual, this is the procedure about OXYGEN (O2) SENSOR:
The O2 sensor is located in the right exhaust downpipe below the exhaust manifold flange (Fig. 18).


REMOVAL
WARNING: THE EXHAUST MANIFOLD BECOMES VERY HOT DURING ENGINE OPERATION. ALLOW ENGINE TO COOL BEFORE REMOVING OXYGEN SENSOR.
(1) Raise and support the vehicle.
(2) Disconnect the wire connector from the O2 sensor.


CAUTION: When disconnecting the sensor electrical
connector, do not pull directly on wire going into sensor.
(3) Remove the O2 sensor from the exhaust manifold.


INSTALLATION
Threads of new oxygen sensors are factory coated with anti-seize compound to aid in removal. DO NOT add any additional anti-seize compound to the threads of a new oxygen sensor.
(1) Install the O2 sensor into the exhaust manifold. Tighten to 30 NIm (22 ft. lbs.) torque.
(2) Connect the O2 sensor wire connector.
(3) Lower the vehicle.





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The DTC (Data Trouble Code) P0135 is for the O2 sensor Heater Circuit Bank 1 Sensor 1. Bank 1 will always be the cylinder bank with the number one cylinder and spark plug, and the number one O2 sensor will be located before the catalytic converter and usually at the rear of the exhaust manifold or just after it. According to the firing order diagram bank one is the cylinder bank that is closest to the fire-wall and there should be an O2 sensor located there around the rear of the exhaust manifold or just after it. If the engine is a 4 cylinder then it will be the O2 sensor before or up-stream of the catalytic converter. Check for any damaged wiring or loose wire connector at the O2 sensor and if they are alright then replace the O2 sensor and then re-set the check engine light. (The auto part store should re-set the check engine light for you if you purchase the O2 sensor from them, and be certain that it is the correct and assembled O2 sensor for your vehicle and not a put together universal O2 sensor)

Why would you need a diagram?

You simply need to educate yourself

O2 Sensors have been on vehicles over 25 years,and in the same place

Sensor 1--in exhaust pipe before converter or in converter
Sensor 2 in outlet of converter

An O2 Sensor Code---Does Not mean replace it

The only way that it will most likely come loose is to first soak the base of that O2 sensor in a good penetrating oil (liquid wrench, pb-max, wd-40) for a while before you attempt to remove the O2 sensor, then use a large 7/8" six-point box-end wrench (it will fit into a lot more spaces than an O2 sensor socket and a ratchet, and you will be able to apply a lot more torque to the O2 sensor) and cut the wire connector off of the old O2 sensor if the box end of the wrench does not slip over the wire connector. Once the box end of that wrench is firmly on the base of the O2 sensor you should have little problem getting that O2 sensor loose, and tap the end of the wrench in the direction to loosen up the O2 sensor using a small mallet if necessary (it never has been necessary for me, and the palm of my hand has always been sufficient).

You will have to use proper judgment, because if you can get the box end of the wrench described above on that O2 sensor you will be able to apply enough torque to break the O2 sensor off at the bung, or even rip the entire bung out of the ehaust manifold or exhaust pipe, but you would have to be really tugging on the wrench or beating on the wrench hard with a mallet to do so.

When you install the new O2 sensor be careful not to over-tighten it.

Bank #1 is always the cylinder bank that has the #1 cylinder and spark plug in it, and O2 sensor #1 is always the first O2 sensor in the exhaust system, and is either on the exhaust manifold itself, or just after the exhaust manifold on the exhaust pipe. Here is a diagram and bank #1 is composed of the #1, #3, and #5 cylinders and it is the exhaust closest to the fire-wall.

Actually, you have two oxygen sensors: primary is in the exhaust manifold(under hood, center, lower engine area, above exhaust pipe flange, mounted in exhaust manifold) and the secondary is in the catalytic converter.
Since the sensor has a electrical wire on it to connect it to its connector, you will need a special wrench to remove it; they can be rented, I believe, at Autozone. Also, they tend to be quite difficult to get started for removal since they are in a manifold that gets very hot then cools down again and again.
Hope this helps you.

P1135 means that your O2 sensor has gone bad. The O2 sensor on the Toyota's are called Air fuel sensor's. If you have a 4 cylinder engine, the O2 is on the exhaust down pipe before the catalytic converter, and if it's a V6 it the O2 sensor on the fire wall side along the down pipe from the exhaust manifold. (sensor 1, bank 1) Good luck and keep me posted, check the wire harness. The wire harness could have corroded or burnt from the exhaust, but most likely it's going to be a bad O2. Keep me posted ,be glad to help

I just got done replacing the O2 sensors in my 99 Cougar due to throwing a P0135 malfunction code. There's 3. Facing the engine there's one in the front coming off of the front header, which is easy to get to. Another more tricky one if between the engine and the fire wall on the rear header pipe. The third is under the vehicle behind the transmission pan on top of the exhaust. In order to replace the O2 sensor near the fire wall you will need to remove the 4 retaining bolts for the ECM module and move it out of the way. Additionally you will need to remove the 2 retaining nuts for a wiring harness that is seated below the ECM module. Pay close attention to the connectors because the front and under vehicle O2 sensors have round connectors the one near the firewall has a squared connector. I was able to replace all 3 by myself in approximately 35 minutes. If your throwing a O2 heater malfunction code it is most likely going to be the sensor near the firewall. make sure that you know someone with a code reader so the code can be cleared. If you're do for an emmissions inspection be sure to put at least 40 miles on the new O2 sensor with different types of driving (e.g. highway, coasting, decellerated turns and rapid acceleration). Gotta love project cars for your kids!!

Usually the O2 sensor will be on the exhaust manifold close to the engine, I'm going to assume you have a pretty good idea of what you are doing so if you need more details don't hesitate to ask.