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Oxygen sensor - I'm baffled 200 1989

posted by  someone claiming to be Vabuckeye on  Sat Apr 5 14:43 CST 2003 [RELATED]

I just bought a 1989 245 with 153k and a manual trans. It runs perfectly and gets 28 mpg. The check engine light was on when I bought it and it displayed the 2-1-2 oxygen sensor code. When I erased the code it would come back after about 5 miles. The previous owner gave me a used oxygen sensor. I installed it and it still runs perfectly, & now it takes 50 - 500 miles for the light to come on and display 2-1-2. O2 sensor voltage is .568 and it fluctuates very little - goes to .570 if I rev it. Given how well it runs, I'm tempted to remove the check engine light bulb & forget it, but what would it take to fix it?








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    Oxygen sensor - I'm baffled 200 1989

    uid 27's pic
    posted by  Art Benstein on  Sat Apr 5 15:18 CST 2003
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Fri Oct 17 20:10 CST 2014
    [RELATED]

    Great mileage! Almost seems like your car is in trim without the feedback.

    The code is being set because the computer doesn't see the quick switches between lean and rich it expects as the sensor reads and the computer compensates. It only sees the offset voltage being provided by the computer itself so it thinks you have no oxygen sensor.

    I'm not sure what conditions you're measuring under, but I believe the sensor has to be heated to provide any measurement being so far away from the manifold in the '89, so it is possible the heater circuit isn't getting juice. Best way to check that is to run it for a few minutes, then pull the heater connector and quickly measure the heater resistance. You'll see it falling rapidly from some value above 10 ohms to maybe less than 4-- the actual numbers aren't that important, just the fact the resistance drops significantly tells you it was hot and now is cooling. If the resistance is steady you probably don't have 12V getting to the heater connector or a pin has pushed back.

    If the heater is OK and you still get a fairly steady 1/2 volt out of the sensor, it is open. Could be the wire, or the element is broken inside the downpipe. To tell for sure, disconnect the sensor (green wire part) from the computer and check you have that same 1/2 volt coming from the computer but not from the sensor.

    The clue that it might take 500 miles to set the light tells me to suspect the heater circuit: a good hard drive might get the sensor going without the heater, so it is just the idling and slow driving that the computer is complaining about.
    --
    Art Benstein near Baltimore








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      Oxygen sensor - I'm baffled 200 1989

      posted by  someone claiming to be Vabuckeye on  Sun Apr 6 13:43 CST 2003 [RELATED]

      Thanks for the analysis, Art. You were exactly correct that the heater was the problem. Once I saw it was getting no voltage, the rest was easy - the fuse was missing. I put in a fuse, and the O2 sensor voltages started fluctuating like they should.








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        Oxygen sensor - I'm baffled 200 1989

        posted by  someone claiming to be Also240Owner on  Mon Apr 7 09:58 CST 2003 [RELATED]

        Can you tell me where is the fuse located ? Also where to check the voltage ? is it right from the the connector ( one 2 wires and the other is 1 wire under hood ), I have the exact problem and installed a new O2 senzor the problem still, thanks








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          Oxygen sensor - I'm baffled 200 1989

          posted by  someone claiming to be vabuckeye on  Tue Apr 8 00:38 CST 2003 [RELATED]

          It's the #4 fuse in the panel by the front door where all the fuses are. The only other thing on that fuse is the in-tank fuel pump, which you might not notice isn't working. I checked the O2 sensor voltage at the one wire connector under the hood near the hinge. Just peel back the rubber cover and attach the voltmeter probe to the connection. The 2-wire connector is for the heater - one wire is 12 volts, the other is ground. Measure the female end of the connector.








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            Oxygen sensor - I'm baffled 200 1989

            posted by  someone claiming to be Also240Owner on  Wed Apr 9 05:10 CST 2003 [RELATED]

            I found the #4 fuse surely it was blown, replaced the fuse reset the Check Engine Light, now I am waiting to see if the light comes on again, ( usualy it come on after 40-50 miles of driving.....
            Thanks very much.







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        Oxygen sensor - I'm baffled 200 1989

        uid 27's pic
        posted by  Art Benstein on  Sun Apr 6 15:48 CST 2003
        Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
        last visit: Fri Oct 17 20:10 CST 2014
        [RELATED]

        Thanks for posting an update. I had no idea there was a separate fuse for the oxygen sensor heater on the 89.

        --
        Art Benstein near Baltimore







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