O2 sensor location

My 2001 SEL 3.0 DOHC Taurus is giving me a P0136 code which is a O2 sensor down stream of the catalytic converter. This car seems to have 4 Ov sendors. Can anyone tell me exactly where this on is? I see one after the converter which is right berlow the oil filter but there is another on further down after a Y pipe. That one is covered in oil from a leak I hasve and my guess is that is probably the bad one but I want to be sure before I go through the trouble
Thanks

My 2001 SEL 3.0 DOHC Taurus is giving me a P0136 code which is a O2 sensor down stream of the catalytic converter. This car seems to have 4 Ov sendors. Can anyone tell me exactly where this on is? I see one after the converter which is right berlow the oil filter but there is another on further down after a Y pipe. That one is covered in oil from a leak I hasve and my guess is that is probably the bad one but I want to be sure before I go through the trouble
Thanks


P0136FordO2 Circuit (Bank 1, Sensor 2)

Bank 1 is always the side that No.1 clyinder is on. This case it is the Bank closest to the firewall (Passenger side)

Sensor 2 means the sensor after the catalytic convertor.

The sensor you need to look at would be after the cataylic convertor on the passenger side of exhaust.


Here is a link that will be helpful to you:

http://www.aa1car.com/library/oxygen_sensor_locations.htm

Check the wires for any breaks.

How many miles on vehicle???


Hope this helps

Car has 129000 miles on it. That is the one covered with oil. I got it out but I can't screw the new one in. The threads look a bit galled. I don't know the thread size to get a tap to chase the threads. Any idea? The replacement is a Bosch

Car has 129000 miles on it. That is the one covered with oil. I got it out but I can't screw the new one in. The threads look a bit galled. I don't know the thread size to get a tap to chase the threads. Any idea? The replacement is a Bosch

I do no t know the size. I would call parts store and ask them they should be able to tell you and have them on hand.

Looking around the internet I found oxygen sensor thread chaser. Only seems to be one size, 18MM x 1.5. So I got it. Getting it in there was not easy. Not more than 4 inches of clearance to work but after 30 minutes cleaned enouogh thread to get the o2 sensor in tight.
By the way does anyone know what the read out on these sensors should be. I got a cable from GoTechnology that connects the OBD to the iPhone and then with a free app you can read all the o2 sensors as well as timing, mass air flow, rpm's and fuel trim (whatever that is). What should these sensors read at idle with a warm engine. I'm getting readings between .250 and .800 volts except for that one bad one which seem to read a steady .430V. Anyway changing the o2 sensor was just another in a long line of sucky jobs to do on this car.

Ok so I have an update and my problem is not solved. With my old sensor I was getting a steady .430V reading. With the new Bosch sensor I'm getting 0V for a reading. Is it possible I have the wrong sensor? Is there a difference between upstream and downstream? I unplugged the sensor, cleaned the connections (had some oil on it) and plugged it back in making sure the connector clicked in place and still getting a zero reading. How can I check to see if the new sensor is bad?
I looked at a website selling oxygen sensors and they have so many choices upstream, downstream, precatalyst post catalyst that I'm thoroughly confused. HELP:banghead:

So after all the trouble putting this sensor in I'm now getting a zero volt reading from it. Did I get the right sensor? The scanner said it is the Bank 1 Sensor 2. Is that the one visible front the right front wheel well. That's how I accessed it. Where is that second catalutic converter. Looks like it's further back in the middle of the underbody but I don't see any sensors after that. If that is not the cat what is it? So confused.

Just wanted to update everyone. I deceided to go ahead and change that sensor again! I swapped out the Bosch with a Motorcraft and now I'm getting normal voltage readings so either I damaged the Bosch sensor putting it in or i got a bum one from the autoparts store. At any rate I cleared the light and all seems to be fine.

By the way since I can monitor my readings while I'm driving on my Iphone I was wondering what they should read on normal driving speed when the car is warm. I read somewhere that readings under .5V indicate a lean condition and over .5 indicate a rich condition. Seems to run richer when I'm driving and lean when I'm at idle.

You're mostly correct on the voltage readings. Since the typical range of an O2 sensor is 0-0.9 V, the mid-point is 0.45V. Above 0.45 is considered a rich mixture while voltages below 0.45 is considered lean.

Some number of years ago I saved off a file from AA1 Car (http://www.aa1car.com/library/o2sensor.htm) that did a pretty good job of explaining oxygen sensors and what you should expect from them. Here's how it explains the function of the downstream sensor:

"The OBD II system monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions, which are also called "crosscounts"). The sensor's voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher.

"If the signal from the downstream oxygen sensor starts to mirror that from the upstream oxygen sensor(s), it means converter efficiency has dropped off and the converter isn't cleaning up the pollutants in the exhaust. The threshold for setting a diagnostic trouble code (DTC) and turning on the Malfunction Indicator Lamp (MIL) is when emissions are estimated to exceed federal limits by 1.5 times.

"If converter efficiency had declined to the point where the vehicle may be exceeding the pollution limit, the PCM will turn on the Malfunction Indicator Lamp (MIL) and set a diagnostic trouble code. At that point, additional diagnosis may be needed to confirm the failing converter. If the upstream and downstream O2 sensors are functioning properly and show a drop off in converter efficiency, the converter must be replaced to restore emissions compliance. The vehicle will not pass an OBD II emissions test if there are any converter codes in the PCM."


-Rod

Thanks Rod,

As usual you are a wealth of information.

Much appreciated