What does O2 sensor do?
 

I also have a code in ECM for the O2 sensor. Is this something I need to address right away? If it is a sensor and not the wiring, are they easy to replace? I know they are cheap, like $30. How hard to install? Where is it located?

Re: What does O2 sensor do? (dbwade36)
 

Once they reach operating temperature (600F) the tell the ECM if the car is running lean or rich and the ECM adjusts fuel accordingly.

They are not too hard to replace, they are located on your exaust just before your cats most likely. The screw in and will have a wire leading out of them to the ECM.

Re: What does O2 sensor do? (dbwade36)
 

Basiclly the O2 reads the gases in the exhaust stream and passes on the info in way of voltage to the ECM. The ECM ignores this info in open loop however in closed loop the computer adjusts the fuel delivery (pulse width to the injectors) based mainly on the O2 sensors. They are located in the exhaust pipes just below the manifold. Fairly straight forward to replace. You can use a shorty 7/8" wrench or buy the O2 tool which fits over the sensor and is rachet driven. If your throwing codes that relate to the O2 then I wouldn't let it go on to long as your fuel mixture will be affected.

Re: What does O2 sensor do? (dbwade36)
 

As mentioned, the O2 sensor rules; without it the ECM will not go into closed loop mode. You should replace it soon.

It's located in the side of the left exhaust Y-pipe, just below the manifold. You'll see the wire going to it.

Spray some Liquid Wrench on it but clean up the area before installing the new one; and don't touch the business end of the new sensor.

Re: What does O2 sensor do? (dbwade36)
 

Like they said, the 02 sensor is critical to engine performance. Your mileage will drop significantly usually.

Replace it as soon as possible.

Re: What does O2 sensor do? (vader86)
 

how do you check if it is bad if it doesn't throw a code?

Re: What does O2 sensor do? (konroh)
 

Theres a tool they sell in some of the magazines for it, but usually when your avg mpg drops significantly then its the O2 sensor going out. They dont always throw a code.

Re: What does O2 sensor do? (vader86)
 

How many o2 sensors do we have. Do different year C4's have them in different places. Just seems like there should be more than one.

Re: What does O2 sensor do? (OleDog)
 

Early C4's had one on the Dri side down pipe.

Threads should already have Antisieze on them. This is a good thing. It helps the next guy replace it.

Re: What does O2 sensor do? (ZylaRace)
 

I will be replacing O2 sensor tmw, most likely. My milage has suffered some. The codes were cleared yesturday and it threw code again today after about 20 mins of driving. So, I am just going to get new one.

Re: What does O2 sensor do? (dbwade36)
 

I don't know exactly how an O2 sensor works, but I can guantee you it does not read the gases. If you look at it, its the most primitive sensor you'll ever see.

I believe it reads the temperature of the combustion, which should be between two temperatures, probably about 500 degrees and 675 degrees, or something like that. If it gets to hot, there is too MUCH air, if it gets cold, there is too much fuel.