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Motronic 2.7 self diagnostics

Discussion in '456/550/575' started by Dr1ve, Aug 27, 2025 at 10:17 AM.

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  1. Dr1ve

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    Feb 2, 2022
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    Ole-Jakob Nilsen
    #1 Dr1ve, Aug 27, 2025 at 10:17 AM
    Hi all!
    I would like to flash some codes in on the dashboard, but my 1995 456 GT does not have the diagnostic push button on the ECU.

    There are 3 plugs coming out from the main loom, a 3-connector which I presume is for the SD-1 and two single connectors with a blue and black wire.

    Any knowledge on which wire I should short to ground - preferably without frying the ecu?

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  2. Dr1ve

    Dr1ve Rookie

    Feb 2, 2022
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    Ole-Jakob Nilsen
    #2 Dr1ve, Aug 27, 2025 at 10:18 AM
  3. Qavion

    Qavion F1 World Champ
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    #3 Qavion, Aug 27, 2025 at 5:50 PM
    I only have one wiring diagram for the 456GT (2.7), and that is the Left Bank Engine diagram. It shows the following:


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    HN = grey with black stripe
    N = Black
    HR = Grey with red stripe

    Your colours look different.

    On the Ferrari 348, I have these colours:

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    HR = Grey with red stripe
    N = Black
    HM = Grey with brown stripe.

    That seems to be a better match. Anyway, in either case, just short out the black and grey/red as per the test procedure.

    In the diagram, the 456GT blue and black wires are labelled "For excluding idle speed control", whatever that means. They are joined together to produce that effect, but I guess they are not normally joined.
     
    flash32 likes this.
  4. Qavion

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    #4 Qavion, Aug 27, 2025 at 5:55 PM
    Assuming that wire on the right is grey/red...

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    Make sure that you have bulbs in the Check Engine lights. I heard that some Euro cars don't have bulbs.
     
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  5. Qavion

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    #5 Qavion, Aug 27, 2025 at 6:15 PM
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  6. Dr1ve

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    Feb 2, 2022
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    Ole-Jakob Nilsen
    #6 Dr1ve, Aug 27, 2025 at 11:20 PM
    Thanks!
    The 3-pin connector has the correct wires - grey/red and black.

    I got the correct bulbs fitted in the binnacle. I'll have a go flashing codes later today!
     

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