265/75/16 - Speedo Correction





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  1. #1
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    Default 265/75/16 - Speedo Correction

    So I've fitted a set of 265/75/16 AT's today to my Triton.

    The speedo is now dead on according to the GPS!

    My problem is that the VSS signal to the OBC is now not accurate anymore. It under reads by about 5%. This to be expected as most cars speedo's are optimistic for speeding fine prevention purposes. The 5% error however means that the odometer and fuel consumption displays will now have a significant error resulting in a higher than actual fuel consumption figure.

    I've been reading the Triton service manual but can't seem to find anything useful.

    I would guess that the speed sensor is a frequency to voltage conversion setup. So barring a software fix - which I think is unlikely - one would probably have to add some sort of calibration circuit to the speed sensor so that it can be tuned up again.

    Trouble is I can't seem to find circuit diagrams for the speedo and I'm not exactly sure how the setup works so I can't really give my plan a try.

    Anybody have some auto electrical experience that can shed some light on the issue?

    It stands to reason that the factory should also have some way of calibrating the speedo but my guess would be that it might be in software and not as simple as tuning resistor somewhere...

  2. #2
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    It seems the aussies can actually buy different speedo drive gears which would of course be ideal!

    http://www.4wdaction.com.au/forum/sh...d.php?p=827475

  3. #3
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    Hmmm... maybe the odometer has also been under reading, just like the speedo?

    Maybe what you can do is use GPS to measure say 100km (or more) of driving, and compare it to your odometer reading, to check how accurate it is?
    2005 Mitsubishi Pajero SWB 3.2 DiD GLS (sold)
    2008 Mitsubishi Pajero LWB 3.2 DiDc GLS

  4. #4
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    Try speedo services in Germiston - they have done amazing things with my imported cars and are friendly and reasonably priced.

  5. #5
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    Quote Originally Posted by Greg View Post
    Hmmm... maybe the odometer has also been under reading, just like the speedo?

    Maybe what you can do is use GPS to measure say 100km (or more) of driving, and compare it to your odometer reading, to check how accurate it is?
    The odometer has the same 5% error now.

    The speedo is fine, but the OBC speed now 5% lower than it should be.

  6. #6
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    Quote Originally Posted by Daen View Post
    Try speedo services in Germiston - they have done amazing things with my imported cars and are friendly and reasonably priced.
    Thanks! I'll give them a try if I don't find someone in Pretoria.

  7. #7
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    Ok. I've just been to the Bosch Service Center. They say that they can easily fix the speedo by just downloading the OBC memory, adjust the correct setting and voila speed reading fixed.

    It will cost R350.

  8. #8
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    Which bosch service centre is this? I need to get mine corrected also my speedo is quite bad an indicated 120 is actually 124.

  9. #9
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    Cencar in Centurion.

    I will probably take mine next week or so...

    c/o Lenchen & Jacaranda Street,
    Lenchen Park, Shop 12
    Telephone: 012 653 3155
    Fax: 012 653 5132
    Email: [email protected]
    Manager: Carlo du Plessis
    Last edited by Cobus80; 2010/08/12 at 01:20 PM.

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