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  • [Corsa D] Corsa D Emissions Test Failure

    Hi I am new to the forum, and would like some help please with an annoying problem! Not sure whether this should be in Electrical or Mechanical, but since sensors are involved, I posted it here. Hi - my Vauxhall/Opel Corsa has failed the MOT test due to high emissions! This car passed the test with flying colours in 2017, but about 6 months ago was intermittently giving poor running and DTC codes relating to O2 sensor, lean mixture, lean mixture at idle, etc.... I Changed the o2 sensor, but faults returned intermittently. Sometimes it would run OK for weeks without problems… On the advice of a local mechanic, I cleaned the intake manifold and throttle body, and cleared the codes. The car now runs fine, but when the emissions were tested, they were out by a mile! - e.g. CO TEN TIMES the limit, HC, 50ppm over the limit! I have been going through the sensors. The Air Intake sensor is OK (resitance changes significantly with temperature), the MAP sensor (it doesn't have a MAF sensor) is OK (1.1V at idle, 3.9V when revved), The top O2 sensor has been changed twice now, once by me and once by a local garage. I have now refitted the original one, after testing it with a blow-lamp. Any ideas what I should check next? I haven't checked bottom O2 sensor, or coolant temperature sensor, but would these have such a significant effect? What can be causing such a massive increase in emissions? Thanks in advance for your help!

  • #2
    Hi Welcome to the forum
    From what you've changed and your ability to test it, its quite likely you know more than me in this area . But I would have thought the coolant temperature sensor could be significant. If the ecu believes the engine is running colder than it really is it may be metering the air fuel mixture too rich.

    But I dont know why the O2 sensors are not detecting it is running rich or whether this is enough for your emission test readings.

    What is the condition of the spark plugs? If they are sooty black this is further confirmation the mixture may be too rich. But gets you no further forward as to the reason.

    I believe with the correct equipment an expert can read various ecu parameters and measurements that might give better idea of what is wrong. But this is getting into the realms of remapping etc (and computers) of which I know little . But eventually the cost of speculatively replacing sensors etc in the hope of a cure might exceed the cost of professional help.

    But if like me you like to 'have a go' before admitting defeat there is a way you may be able to test the water sensor without removing it. I believe its possible to read a 'hidden menu' on the cars dashboard display, which I think includes water temperature. If when you know the engine must be very hot (100c+ maybe) but the display is showing a significantly lower water temperature the sensor may be giving a false reading.

    But I have never used the hidden menu so you would need to research how to do this this yourself.
    Last edited by Bugman; 27-07-2018, 10:45 AM. Reason: Thought of a cunning plan

    Comment


    • #3
      Welcome to the Forum.

      As I posted elsewhere recently, I once came across a plastic bag that had found its way into the air intake and thrown the system into turmoil - A long shot I know, but worth a check for all that.

      I have never heard of testing an O2 sensor with a blowlamp, but am intrigued - can you expand on that one please.

      Many times, I have come across cases where people (including garages) have changed various types of sensor, only to find that there is no improvement - or even found to have made the matter worse. This is invariably due to fitting spurious (cheap) sensors. I always recommend people to use only GENUINE sensors.

      If the CO level really is 10 times the limit, the car should not be, as you say, 'running fine'. I would suggest that you have a look at the inside of the tail pipe - Does it have a 'sooty' coating inside it? As Bugman suggests, it might be worth taking out the spark plugs (preferably after a fair run) and looking at their colour/condition. My thinking here (another long shot maybe) but it is possible that the MoT equipment is/was not correctly calibrated - If all else fails, it might be worth asking another garage to check the CO levels for you.

      Regards

      Comment


      • #4
        Originally posted by Bugman View Post
        Hi Welcome to the forum
        From what you've changed and your ability to test it, its quite likely you know more than me in this area . But I would have thought the coolant temperature sensor could be significant. If the ecu believes the engine is running colder than it really is it may be metering the air fuel mixture too rich.

        But I dont know why the O2 sensors are not detecting it is running rich or whether this is enough for your emission test readings.

        What is the condition of the spark plugs? If they are sooty black this is further confirmation the mixture may be too rich. But gets you no further forward as to the reason.

        I believe with the correct equipment an expert can read various ecu parameters and measurements that might give better idea of what is wrong. But this is getting into the realms of remapping etc (and computers) of which I know little . But eventually the cost of speculatively replacing sensors etc in the hope of a cure might exceed the cost of professional help.

        But if like me you like to 'have a go' before admitting defeat there is a way you may be able to test the water sensor without removing it. I believe its possible to read a 'hidden menu' on the cars dashboard display, which I think includes water temperature. If when you know the engine must be very hot (100c+ maybe) but the display is showing a significantly lower water temperature the sensor may be giving a false reading.

        But I have never used the hidden menu so you would need to research how to do this this yourself.

        I don't really know very much about what I am doing (Lol!) - but I have an electrical background and a meter, and my way of thinking is if I can test all the sensors, I will hopefully find one which isn't working correctly. The trouble is I have already tried most of what I consider to be the likely suspects!



        The coolant sensor is a good one, and I will try that one next! - I almost forgot that there is no coolant temperature display on the dash - first time I have seen this missing on a car I have owned!. Thanks for the help and advice!

        Comment


        • #5
          Originally posted by walksall View Post
          Welcome to the Forum.

          As I posted elsewhere recently, I once came across a plastic bag that had found its way into the air intake and thrown the system into turmoil - A long shot I know, but worth a check for all that.

          I have never heard of testing an O2 sensor with a blowlamp, but am intrigued - can you expand on that one please.

          Many times, I have come across cases where people (including garages) have changed various types of sensor, only to find that there is no improvement - or even found to have made the matter worse. This is invariably due to fitting spurious (cheap) sensors. I always recommend people to use only GENUINE sensors.

          If the CO level really is 10 times the limit, the car should not be, as you say, 'running fine'. I would suggest that you have a look at the inside of the tail pipe - Does it have a 'sooty' coating inside it? As Bugman suggests, it might be worth taking out the spark plugs (preferably after a fair run) and looking at their colour/condition. My thinking here (another long shot maybe) but it is possible that the MoT equipment is/was not correctly calibrated - If all else fails, it might be worth asking another garage to check the CO levels for you.

          Regards

          I have checked and cleaned the intake piping and removed and cleaned the throttle body. I also squirted some carb-cleaner around the intake manifold, which was quite black/sooty...The first time I started it up, there was a big cloud of black smoke!.....

          I tested the O2 sensor by metering between two pins (signal and ground) and heating it with a blow torch, whilst measuring the resistance. Once hot, the reading should change significantly, depending upon whether the sensor is in the flame (low O2) or in free air (High O2). I did this and it seemed to be doing what it should.....

          As for the emissions results, they were as follows:

          CO: Max permitted = 0.2% 2016 result = 0.000% 2018 result = 2.06% !!!
          HC: Max permitted = 200ppm 2016 result = 31ppm 2018 result = 254ppm !!!
          Lambda - 0.97-1.03 2016 result = 1.011 2018 result = 1.030

          So as you can see - massive differences! The car has probable done less than 2,000 miles between these tests, so it is unlikely anything in the engine has changed, and as I say the car does (surprisingly!) drive very well!



          Comment


          • #6
            Update - tested the coolant sensor (via the display in the "Hidden Menu" on the dash) - all fine! Checked bottom O2 sensor, but couldn't unscrew it from the exhaust to test. However, I did undo the connector and found it to be full of OIL! Could this be the problem? It looks as though oil is getting in via the inside of the loom leading to it (not sure from where?) Oil doesn't seem to be leaking out of it down the wires to the sensor, but oil in the connector can't be good surely? I have washed the oil out with contact cleaner spray and left to dry thoroughly....When I re-connect I might see whether friendly garage will re-run the emissions test for me?

            Comment


            • #7
              I seem to remember a spate of this oil contamination on here quite some tome back, but can't remember where the oil was getting in from - it might be worth a search back to see if there is any help to be found.

              Regards

              Comment


              • #8
                It gets into the wire loom from the oil pressure switch. Sometime ago the oil switch must of been leaking, and if you don't noticed it early , it will push the oil all round the engine wiring loom . If it's got to the back sensor I'm guessing it's in the plug of the ecu. take the plug of the ecu and see if there's oil in the ECU. If there is you'll have to clean it out best you can with a solvent . But be careful inside the ECU as the pins are tiny.

                Comment


                • #9
                  Originally posted by Restorer View Post
                  It gets into the wire loom from the oil pressure switch. Sometime ago the oil switch must of been leaking, and if you don't noticed it early , it will push the oil all round the engine wiring loom . If it's got to the back sensor I'm guessing it's in the plug of the ecu. take the plug of the ecu and see if there's oil in the ECU. If there is you'll have to clean it out best you can with a solvent . But be careful inside the ECU as the pins are tiny.
                  Bingo!

                  Yes - the oil pressure switch was leaking, and I replaced that a couple of months ago! That would certainly explain the source of the oil! I haven't checked out the ECU yet, and not entirely sure where it is? I'm told it is on the manifold, on the right side of the engine? Can't see it directly though! Will have to get the mirror out! - I'll check it out as my next step! Thanks!

                  Comment


                  • #10
                    Yes it's on the side of the inlet manifold. Don't attempt the ECU if your not confident. Taking off the wire plug is fairly easy. But putting it back on , everything must be line up , as if it's not the plug will still go on , but will bend the tiny pins flat . There's two plugs on the ECU, the top one is the engine wire loom and the bottom one is fed from the fuse and relay box .

                    Comment


                    • #11
                      I managed to locate the ECU and remove the connector. It was full of oil, as are most of the other connectors! What sort of rubbish design allows oil to get into the loom and connectors like this? It is certainly an eye-opener for me (coming from an automotive background) as I thought these connectors were supposed to be sealed!

                      I have flushed out the following connectors with contact cleaner.


                      ECU
                      Top O2 Sensor
                      Bottom O2 Sensor
                      MAP sensor
                      Electric Throttle controller
                      and whatever that 3 -pin connector is on top of the cam cover!

                      I will let them dry out, repeat, then re-assemble. Then I might try to get the emissions test done again, in the hope that I might have fixed it!

                      Thanks to everybody for their help!

                      I'll let you know how I get on!

                      Comment


                      • #12
                        I cleaned the oil out of all the connectors by repeated flushing with contact cleaner and allowing it to dry out, over several days. I am now confident that all the connectors are now clean.

                        But a thought occurred to me: Why should oil in the connectors even matter? Engine oil is an insulator, right? so I conducted a little experiment:

                        I measured the resistance of clean new engine oil, some used oil from my motorcycle I had hanging around and finally a sample from the Corsa dipstick. In all cases, the meter read "open circuit" which indicates a resistance of greater than 20MOhms! So according to my experiment, even used oil is an insulator, so shoudn't affect the readings of any of the sensors

                        Does anyone have a convincing theory why oil in the connectors should actually matter?

                        Comment


                        • #13
                          I don't know why . But I've done quite a few now where the car is either cutting out , or the fuel trims are all over the place. Like you I've spent many hours of cleaning. And managed to turn them back around. Hope it's sorted.

                          Comment


                          • #14
                            Originally posted by Restorer View Post
                            I don't know why . But I've done quite a few now where the car is either cutting out , or the fuel trims are all over the place. Like you I've spent many hours of cleaning. And managed to turn them back around. Hope it's sorted.
                            Thanks - I read a theory on another forum that the oil can get into the heaters on the O2 sensors and make them miss-read! I don't know whether this is true or not, but it could explain why changing the sensors sometimes fixes the issue (until the oil affects the new ones, if the pressure switch is not replaced as well?)

                            I am tempted to ask for an emissions check as is, and if it fails again - replace top and bottom O2 sensors.....I will also be on the lookout for any remnants of oil trickling through and reaching the connectors again!

                            Comment


                            • #15
                              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.

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