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Thread: MOT failure questions

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  1. #1
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    MOT failure questions

    My wifes 2009 ForTwo non MHD Turbo Highstyle failed the MOT yesterday.

    It failed on a number of issues which the test centre said were probably because she does not take it out often enough.
    In the last 12 months she has driven 1300 miles and the failures were

    - severely reduced offside front headlight strength
    - rear brake binding
    - exhaust emissions lambda outside limits
    - exhaust emissions carbon monoxide excessive
    - rear tyres excessively cracked

    The tyres I will replace and the rear brake I will strip and clean (which is what they suggested it probably needs)

    However, they suggested
    - that the exhaust emissions probably indicated that the cat needed a clean and that I put some cat cleaner in the fuel and run for a few miles to clean it,
    -I try a new bulb in the headlight to see if that was the problem and if it didn't then the unit would need replacing.

    So my questions are
    - is it likely that a cleaner will cure the emission problem, and which should we use, or is it more likely to need a new cat.
    - I tried a new bulb with no change, so is there any way to 'repair' the reflection from the headlight unit, or will it need replacing.

    Hopefully some of you have had similar issues and can advise on how you dealt with them.

    Thanks.

  2. #2
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    Re bulb - I'd check that the earths are in good order. That's assuming the bulb is just dim. If the reflector has (somehow) failed, then probably new light unit required.

    Re cat - the subject of cat cleaning is an internet constant. Google a brand name of a cat cleaner (CatAClean?) and trawl the forums for results from those who have used it to ascertain chance of success. Heat, is what cats need, so perhaps a decent prolonged run will help. When was it last serviced? A blocked air filter won't help and if the spark plugs are due replacement then possibly contributing.
    Don't know the cost for a 451 but a complete (with cat) exhaust for a 450 can be had for £100 and will last at least a couple of years.

  3. #3
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    With regards to the emissions failure I tend to use Millers Petrol Additive just follow the instructions on the bottle, you can even double up on the dose for m.o.t. purposes. It will clean your injectors fuel pump, fuel lines etc and lower emissions, once added take the car out and give it a good thrashing for several miles, should do the trick.
    And as pinger suggested check the air filter and if in doubt fit new.

  4. #4
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    Thanks guys.
    Will check the earth as both reflectors look the same (condition) to me.

    I have ordered some cataclean (very cheap, comparatively) from Eurocarparts and will check the airfilter. Then I have to find a way/opportunity to run the car without falling foul of Mr Plod.

  5. #5
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    Dec 2015
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    Looks as though you've got things sorted. Be aware that replacing the rear tyres with new, may bring on the ABS/Traction lights, if the front tyres are low. If so replace them as well, before going down the track of ABS problems. As to the cat, has it been 'fed' leaded fuel, ie avgas? Smarts should only be fed unleaded fuel and the 100/110 octane fuel (race car fuel or Avgas) can have lead in it.
    Lead kills a cat. As to cleaning the cat with cataclean, worth a try. Even with reg plate recognition I'd suspect it would take more than a day for them to catch up with you and by that time you should have your MOT? Are you not allowed to test your repairs before going back for re inspection?? How far are you from an M road? I'd suggest sitting just under 70MPH for an hour in 4th gear. If that doesn't provide enough heat to wake the dead cat, then you've got a dead cat or faulty sensors?
    To the head lights, it may be that the bulb is not sitting correctly in the housing? Do both reflectors look the same, after all, they are just fancy mirrors so you should be able to see that they reflect the same, if one is 'duller' than the other, then that's your problem. Do both bulbs glow the same? Are both bulbs the same part number? Do they both look the same, some have a blue or green or yellow tinge to the glass. Whenever handling light bulbs, you should NEVER touch glass with your bare hands - the moisture from your fingers reacts with the glass when they are on (lots of heat). Have you tried swapping bulb sides? Are the head light lens both clean and clear or dull? If so, head light lens polish should do the trick. If you parked your car about 10 feet from a wall and turned you head lights on, do both light 'patterns' appear at the same height from the ground? The left light pattern should be just slightly higher than the right light, on the wall. If your lights are the same brightness - looking at the light, not the wall, then I'd suspect an alignment problem. Assuming your lens and reflectors are good and look the same. Has the head light bulb been replaced or the headlight assy., had a 'nudge' since the last MOT? If you're really keen, assuming both bulbs are the same, measure the current each bulb draws - it should be the same, if not, there's a restriction in current flow in the car's wiring - good luck finding that. That'd be the whole front panel off and inspecting the wiring from the bulb to the SAM. But, I'd suspect bulbs or bulb seating in the light assy. But wait, there's more - do you have head light height adjustment, as the 450 model does??? If you do, try using that to see if the headlights do adjust up & down, it may be one adjustment motor is dead or stuck. If you have to get another headlight assy., make sure it is for a RHD model NOT a LHD model. - Different light patterns. Happy Smarting. Cheers, Ian.

  6. #6
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    Quote Originally Posted by mad smart person View Post
    If you're really keen, assuming both bulbs are the same, measure the current each bulb draws - it should be the same, if not, there's a restriction in current flow in the car's wiring
    Simply checking that there is 12volts across each bulb at the connector would have precisely the same effect , and you wouldn’t have to cut into the wiring either.

    Any ‘restriction’ in current flow as you say, would simply be down to a excess volt drop in the rest of the supply route back to the battery on both the feed and ground return.
    If there is substantial (and unusual) circuit resistance, then that would result in a ‘lower than battery voltage’ volt drop across the bulb, so you will be able to check the integrity of both feed and earth return simply by checking volt drop across the bulb. (It should be ~battery volts)
    You're so money supermarket and you don't even know it!

  7. #7
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    Quote Originally Posted by pinger View Post
    Don't know the cost for a 451 but a complete (with cat) exhaust for a 450 can be had for £100 and will last at least a couple of years.
    Re Lambda sensor. Probably it is alright, but removing them can be a proper sod. But, you can cut it out of the old exhaust if necessary.

  8. #8
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    Quote Originally Posted by pewe View Post
    - exhaust emissions lambda outside limits
    - exhaust emissions carbon monoxide excessive
    What were the actual values reported? A high lambda value (over 1.00) coupled with high CO is most often caused by an leak in the exhaust system. The leak pulls in air (which causes the high lambda reading) and the cars oxygen sensor sees the air as a weak mixture so adds more fuel which causes the high CO emissions. If lambda is under 1.00 with high CO then either the cat isn't working well, or there is another problem such as a duff coolant temperature sensor.

  9. #9
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    Sorry for the delay in replying - been away for the weekend.

    Here is the report from the MOT station
    mot.jpg

    They said that the emission values were dropping in and out of the required levels, and he did not find any leaks - or if he did they were not mentioned.
    Attached Images Attached Images
    Last edited by pewe; 22-01-2018 at 11:12 AM.

  10. #10
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    That's a pretty marginal fail. If you have an ODB scanner that can read live data then I would see how quickly the oxygen sensor is switching, it should be at least 1 per second, ideally double that. They become very sluggish with age, particularly when operating temperatures are low (i.e. idle and light throttle no load conditions) and can cause this kind of problem.

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