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O2 Sensor check question 200 1993

posted by  Mark Lundell on  Thu Jan 17 06:05 CST 2008
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last visit: Sun Sep 14 21:34 CST 2014
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I checked the O2 sensor from the connector under the hood using my multimeter. When I unplugged the connector and measured directly between the sensor wire and ground, the values went approxamately from .840 to .900( I think this is normal). However with the sensor wire connected properly to the car meter would briefly flash the above values and then change to some completely strange numbers, and then back to the correct values, and then back to strange values...... What gives? One of my manuals says to measure it the second way. Also the check engine light did not come on when the sensor was disconnected.

Thanks for your thoughts.








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    O2 Sensor check question 200 1993

    posted by  vvpete on  Thu Jan 17 07:58 CST 2008
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    last visit: Thu Jul 10 14:10 CST 2014
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    The correct test for the sensor is measuring voltage on the sensor wire while plugged in and the car running after warm-up. It should read 0.4 to 1.1 volts and fluctuate or 'hunt' in a cyclic manner, up and down. When you first start the car up cold it will read 0.8-0.9 volts and hold steady until it warms up then will start to flucuate.
    Reading voltage or resistnce while unplugged won't tell you anything of significance.
    --
    '89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89








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      O2 Sensor check question 200 1993

      posted by  Mark Lundell on  Fri Jan 18 05:21 CST 2008
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      last visit: Sun Sep 14 21:34 CST 2014
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      Should reading constantly show a value within the range. What sbout the bizzare numbers? (I have no reason to suspect a faulty meter)

      Thanks,
      Mark








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        O2 Sensor check question 200 1993

        posted by  lucid on  Fri Jan 18 05:41 CST 2008
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        last visit: Fri Oct 24 12:31 CST 2014
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        "Should reading constantly show a value within the range."

        No. When the sensor is connected, and everything is working right, you should see a rapid flashing of numbers. That's the sign of the sensor and ECU working together to keep the mixture in the correct range (a nominal 0.5V).

        But that 0.5V is a "knife edge" goal, and the mixture strays on either side. The O2 sensor tells the ECU which way it's off by raising or lowering it's voltage output, and the ECU responds by making the appropriate correction. This cycle repeats at a rapid rate, hence the flashing numbers.

        My criteria for O2 sensor metering is to see most of the numbers in the .3 to .7 range, with an occasional .2 or .8 and no .1s or .9s (well, maybe very rare .1s or .9s).

        It's not easy to read the numbers with a good sensor, you just try to scan for those extremes. If the numbers flash slowly, its probably because the sensor is old and slow.


        --
        Bruce Young
        '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.







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