I am getting code PO133. I know it is related to front oxygen sensor. Milage from galon is also down, but how can I tell this is not related to something else like vacume lines? ( Is replacing front oxygen sensor the only option to find out)

Thank you!
1997, 850 T5, 95K

I use the Autoenginuity Scanner. It reports the P0133 as Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1). If you have a high mileage car, I would likely replace it since response of the Oxygen Sensor degrades over time; if not, I would likely disconnect the wiring and spray with some connector cleaner, clear code, and see if it reappears. If it does, then I would replace the oxygen sensor. If the oxygen sensor is not working right, it can cause some cat converter issues.
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1998 Volvo S70

By all means, check all of your vacuum line connectors and elbows. Especially on the passenger side of the intake manifold, that elbow likes to crack and leak.
If your mileage went from 20 to 18mpg around town, then it could also be due to the colder weather.
It is very possible that the front O2 sensor is going bad or has dirt on it from rotten Chicago gasoline :) But, check the vacuum lines first.

Klaus

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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

Thank you Klaus. I knew I could count on your help. You helped me before. I replaced that elbow some time ago - not too much change. My mileage went down from 19 to 14 miles per hour, so I guess I will try to replace Oxygen Sensor. Could you tell me what is the deal with replacing front oxygen sensor. I found one on eeuropart.com and they claim that I have to buy 2 adapters (2 pc of wire). And it does not matter I replace one sensor or both. And I found another oxygen sensor on: www.ipdusa.com

http://www.ipdusa.com/version.asp?strPageHistory=category&numSearchStartRecord=0&strParents=72,170&P_ID=1332&CAT_ID=170&V_ID=2710

and someone claims that this is direct fit. No modifications required.

Also someone recommended me to drive in the city on “3” not on “D”, the same person suggested also that if I take a car on log highway drive on “3” I might overheat oxygen sensor and get rid of buildup and delay replacing oxygen sensor. True or myths???

BOSH, BOSH, BOSH. See the link below

http://volvospeed.com/vs_forum/index.php?showtopic=65824

And yes, if there is buildup in the sensor, a good drive in 2nd gear at about 5,000 rpm can clean it off. If the sensor died, then that won't help.

Klaus
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The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

Thank you very much!