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Corsa D Emissions Test Failure

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  • #16
    Originally posted by Bugman View Post
    I may be taking a simplistic view. But i thought sensors often work by varying their resistance due to changes in temperature, CO2 level or whatever else its measuring, .The the ecu measures these resistance values for its metering, or to detect any that are outside normal parameters indicating a fault. If the circuit has extra resistance due to oil contamination on contacts, the ecu is trying to make sense of incorrect resistance values.
    No, that is exactly right - most of the sensors work that way, or at least by an internal voltage that varies with the properties of the thing being measured (heat, pressure, etc), and yes an external resistance would sway the readings to the point of affecting the running.....But my point is that oil is effectively an insulator and does not conduct electricity. (They use it to cool transformers!) - but then my thought was maybe dirty oil is conductive, since it contains tiny carbon particles - but my little experiment showed that neither clean nor dirty oil conducts electricity, so that cannot be the reason....

    Maybe it gets between the contacts and STOPS them conducting properly? Or maybe it does get into the heater part of O2 sensors and changes the properties as suggested elsewhere?

    There seems to be plenty of anecdotal evidence that oil getting into the wrong places does screw up the electrical system - just trying to understand how?

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    • #17
      As you say, the oil is in effect, an insulator, for that reason, I would have thought that a nice coating of 'insulation' between the sockets and pins of the various plugs, would be the last thing that you need.

      Regards

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      • #18
        Originally posted by walksall View Post
        As you say, the oil is in effect, an insulator, for that reason, I would have thought that a nice coating of 'insulation' between the sockets and pins of the various plugs, would be the last thing that you need.

        Regards
        I think that must be it.....either that and/or the oil getting into the O2 heater elements. I wouldn't think this likely, but until recently, I wouldn't have thought that oil could travel down the inside of wires either!

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        • #19
          Update:

          After cleaning the connectors repeatedly, and running the car a few times, it now appears that the connectors are free of oil! The ECU is now indicating "Heater circuit fault" and "no reading" (or something to that effect) for the bottom O2 sensor, and also sometimes for the top one as well! The sensor connectors seem to have supply voltage on, so I am assuming the wiring is OK.

          I believe that the system is now working properly, and that the ECU is now indicating real faults with the sensors, no doubt due to oil contamination, therefore I have ordered new sensors. In my attempts to remove the bottom sensor, I cut the wiring off so that I could get a ring-spanner on (which didn't help much!...) - and out of interest, cut open one of the wires. To my surprise, it did smell strongly of oil, and when wiping the bare conductors on a tissue, it left a brown oily mark....

          The problems have now moved on to getting the sensor out, and the cross frame bolts, as described in this new thread I have started:

          Removing broken Cross-Brace bolts - TheCorsa.co.uk Forums

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          • #20
            Final update:

            I managed to sort the cross brace out, drop the exhaust and remove the bottom O2 Sensor. I changed top and bottom sensors for quality parts (Bosch and NTK), gave it a run and checked for DTC codes. No Codes, so today I presented it at my local garage for another Emissions test.

            CO has dropped from 2.06% to 0.13% (!)
            HC dropped from 254ppm to 1ppm (!!!)
            Result - PASS!

            The mechanics all had big smiles on their faces, and wanted to know what I had done to fix it!

            Car is now MOT'ed and back on the road!

            Thanks once again for all the advice and help on here - I couldn't have done it without your help!
            Last edited by Corsaman; 16-08-2018, 03:26 PM.

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            • #21
              Thanks for letting us know. Glad you got it sorted.

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              • #22
                Well done Corsaman.

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