Check Engine & O2 sensor or is it?
 

I've checked the archives to see if this issue has been addressed. I'm sure it has but couldn't readily find it. Okay, issue on 98 V70, sudden "check engine" light comes on, car running fine. drive for less than 5 miles then take to mechanic, who uses computer to detect matter: source O2 sensor failure. Set up appt for later this week.
go home, then out again and now the light is off. Is the problem the sensor or a connector. My reading about the O2 sensor and related leads me to think this isn't necessarily a linear matter. Any wisdom to dispense??
My brother says to watch my mileage, if it dips likely the sensor isn't working?

Anytime you get a cel read, write down the code. The car has 2, O2 sensors, front and rear. You need to know which one to replace, they are not cheap. Sometimes the gas milage does not drop but a lot of people ignore them. I usually replace mine with one from a junk yard.

I promies you, if you do a o2 sensor search, you will get 1,000 results.

thx rspi
 

thanks for your comments. yes, I checked prices and can see that the units are not inexpensive. plus as you indicated there is more than one sensor. any clues as to why the sensor light went on... then a day later turned off (without being reset)? Makes me think it may be a connection issue rather than the sensor itself.
My car just passed the smog test in CA recently.
I'm not a mechanic and don't know what the computer said in terms of O2 sensor I or II ?
Help.
Yes, I could see there are MANY issues on O2 sensors.
yikes.

again, get a proper diagnosis pls people before you start to spend any money on parts. what scanner?? (aftermarket AGAIN!!) what is the failure in o2?? (signal missing, too high or low??) or o2 preheating faulty?? what the reading @?? I would find out what's wrong with it first before I spend

o2 sensor in 1998 volvo
 

Thanks for your input. I have not gone to have it "repaired". car is running fine, though perhaps it "misses a bit" on occasion, kind of lags a bit on acceleration, on local street driving not highway. I don't know what the computer that my mechanic used to determine the cause of the "check engine" light that went on. He just said it was the O2 sensor. I didn't have time to address right then, so I went on my way, and later that day the light just went off. So, I don't really know if it a real sensor problem, or a connection issue that righted itself (vibration etc.).
I'll see them next week perhaps and ask more direct questions about the reading of their computer. he plugged in something right at the console in the interior of the car. that's about all i know.
any other insights??