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  1. #1
    Join Date
    Jul 2005
    Spring Park,MN

    System Fault STBD 521-20. ??

    2019 Merc 250 pro xs v8.
    2B596875 is serial
    model is 250LPXSTM
    76 hours
    Basscat Lynx
    24 Fury 4

    smartcraft tack beeps and said “system Fault 521-20”

    was just scanning an area at 5-600 rpm when it went off. I shut it down for a few min. Started back up and it seems ok.

    can you tell me what the code means? I think it got hot. When I turned on temp was like 197 and came down when I started idling around. Drove 15 min and no more warnings. Maybe trash or something plugged intakes......where can I find out what the system Fault 521-10 means?

    Last edited by TonkaCat; 07-18-2019 at 05:27 AM.

  3. Member
    Join Date
    Apr 2019
    Cincinnati, Ohio
    According to this link, I would be lead to believe it is an overheat alarm. Start at page 90.
    2020 Triton 206 Allure
    Mercury 250 Pro XS 4S
    Minn-Kota Terrova 112 w/ IPilot
    Lowrance Ti2 9" console and bow

  4. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Greenville, SC (US)
    +1... Overheating.

    Unless you are certain of the cause, you may want to get this checked carefully. One look at the exhaust section of this engine and you should be able to understand why you do NOT want to be overheating the engine (there are a number of hoses, plenty of wiring and some plastic components in that area of the engine).

    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 44 years (learn something new every day).
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