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O2 sensors and age/mileage S70 1998

posted by  joshturse on  Thu Sep 30 09:47 CST 2004
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last visit: Mon May 21 02:51 CST 2001
[RELATED]

I'm driving a 1998 s70 GLT. The CEL light came on, and I was able to hook up a PC running OBD II software to find out there was a fault - P0172 - rich mixture from the O2 sensor. The kicker is: the car has only 62000 miles on it. O2 sensors are supposed to go bad around 100K, right?

So, I reseated the MAS connection, reset the light. The light has not come back on.

Questions:

What's normal voltage for the O2 sensors?
Do we think dead O2 sensors are a function of age or mileage?
Does my fix make sense?

Thanks,

Josh








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    O2 sensors and age/mileage S70 1998

    posted by  someone claiming to be johnnyl on  Thu Sep 30 11:04 CST 2004 [RELATED]

    100K is when volvo recommends changing them but you see a lot of posts on the BB that shows they can and do fail earlier. Using off brand, no name convenience store gas over time may be a factor as it lacks the cleaning additives of major brands. Go to volvospeed.com (Bay 13) and go thru the vacuum leak detection section first to make sure you don't have a leak that is fooling your sensor into enriching the mixture. I forget the exact voltage but the front sensor will read ~ .3-.8v and will fluxuate rapidly and constantly in that range. You will need a digital VOM to detect the voltage as it is so small. If you have one, disconnect the front O2 sensor connector up in the engine bay and connect your VOM to the black signal lead from the sensor and ground it. Start the engine and see if the above fluxuating voltage is present. ALso check the 200/700 FAQ section as they have a lot of info on troubleshooting sensors.







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    O2 sensors and age/mileage S70 1998

    posted by  the kick inside on  Thu Sep 30 10:57 CST 2004
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    last visit: Thu May 17 09:58 CST 2007
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    now my knowledge on this is mainly 940 based. but bet its the same!

    the 02 should fluctuate from less than 0.5v to greater than 0.5v...and with an analogue meter you should be able to see it do it...

    they way this stuff works (I think!) is that the engine adjusts the mixture according to a pre-programmed map (x much air at y revs = z petrol)...the air part of the equation comes from the MAF sensor... the 02 sensor then looks at (effectively) how efficient the burn is and feeds back into that loop to 'tweak' the mixture...

    I think the MAF sensor works by heating a wire to a given temp and monitoring how much current is required to maintain it..more air = more cooling =more current...but could be measured on resistance i guess

    now seems to me the codes probably just indicate the sensor is detecting perminantly rich mixture...possible casues:-

    1. blown sensor
    2. problem with MAF sensor kiddingthe engine into thinking it has more air than it has...
    3. leak in the pipework if its a turbo (air escaping)
    4. possibly a dodgy MAF connection where the connection results in miss reading...

    sort of makes sense to me...








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      O2 sensors and age/mileage S70 1998

      posted by  joshturse on  Thu Sep 30 16:45 CST 2004
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      last visit: Mon May 21 02:51 CST 2001
      [RELATED]

      Thanks for the input - and I have spoken with my mechanic - Geoff Sheetz, Certified Automotive, Bryan-College Station, TX.

      Few more questions:

      1) The CEL is back on, haven't reset it. After visiting Bay 13 at volvospeed, I notice that a loose MAF/MAS connector can be the culprit, perhaps this is it? Voltage looked pretty good yesterday, between 0.3 and 0.75

      2) Can a driveway mechanic replace the O2 sensors on a GLT? I'm pretty good at figuring things out, but am limited to doing repairs in my parking space (I can't wait to get a garage).

      Thanks for the help!







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