Oxygen Sensor???

tuggy · Post by **tuggy** » 21 Dec 2004, 15:15

Can someone explain what an oxygen sensor does?

Thanks

Tsquared · Post by **Tsquared** » 22 Dec 2004, 18:55

It causes a lot of grief and strife when it decides to stop working.

An O2 sensor measures the amount of oxygen that is present in the exhaust line. There is a sensor above the catalytic converter and one down below the converter. Your computer measures the values gathered by each and the timing and air/fuel ratios are adjusted to give you optimum performance.

If a sensor is malfunctioning and your system is too rich you will have too much gas being dumped into the system causing plug fouling and a smutty exhaust pipe that may blow black smoke. If it is too lean you may have a backfiring through the intake, burnt electrodes/valves, and a white ash exhaust. Both of these examples are extreme and will damage the engine to a degree.

tuggy · Post by **tuggy** » 23 Dec 2004, 00:07

Thanks tsquared. Everything that you mentioned is happing to my car. To much fuel and black smoke/stain all over the back of the car. It runs fine at low RPMs, as stated in my earlier post. Adrian clued me into the oxygen sensor.

Now do you know how to test the sensor before I go out an buy a new one, or is it safe to say that i should just change it out anyway seeing how I am getting close to 100,000 miles on the car and i'm sure that it's the OEM part.

o by the way it's a 97 850 non turbo.

thanks again for all the help. Greatly appreciated.

Post by **matthew1** » 23 Dec 2004, 00:15

You need to read your codes to know which one it is. There's a front and back sensor. To read your codes, you'll need an OBDII code reader -- about $100 -- or have them read by somebody. Volvo dealers, independent mechanics and some parts stores can read codes. I'd call around until you find one that'll do it for free or low cost. It takes 2 minutes, and the reader hooks up to a port under the ash tray.

tuggy · Post by **tuggy** » 23 Dec 2004, 14:02

Thanks Matthew.

I had my mechanic check the car about 2 months ago and the code came back as MAF, so I changed that out thinking it was a "quick" fix. I guess that when a car codes on MAF it could be a bunch of things. I'll get them to recode the computer and see what pops up.

Does anyone know witch one fails more often the front or rear?? Does each sensor have it's own code.

Thanks a ton for the info and this site is truely great source of info.

I'll let you know how I make out.

tuggy

Post by **matthew1** » 23 Dec 2004, 21:46

Yes, each has its own code. Get the number.