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Diagnosing Parasitic current draw - need stock current draw reading

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  • Diagnosing Parasitic current draw - need stock current draw reading

    Hi,

    Just trying to to diagnose a battery drainage issue on a mostly stock 2010 diesel gxl.
    Is anybody able to tell me me what current reading should be with everything off.

    To do this Iím disconnecting the negative terminal on the battery and using a multimeter to measure the current between the battery post and the negative connector.

    I get a reading of 0.13amp, which seems high.
    If I pull the AM2 (7.5amp) fuse in the engine bay the current drops down to 0.01amp.

    Thanks in Advance





  • #2
    I don't have any current measurements for you, but Is AM2 the main body ECU fuse? If so, that thing has all sorts of power saving modes that kick in under certain conditions. Where was the key when you were taking your measurements? If the key has been in close proximity for more than 10 minutes it backs off. If the system hasn't been used in over 5 days it backs off. If the system hasn't been used in over 14 days it backs off even further.

    As an example, with the interior lights disabled via the overhead switch, and the car locked, just walking up to the driver's door with the key in my pocket causes increased current flow. You can see the small voltage dips below.. each one of those corresponds to me standing near the driver's door and then walking away.

    [EDIT] - actually scratch that last bit about voltage measurements. The under car running-board lights still work when the interior lights are off and because I did the test in broad daylight, I didn't notice there were coming on. They'll contribute way more to any voltage drops than the body ECU coming to life. Although the bit about the power saving modes stands, you can read about that in your owner's manual.
    Last edited by dBC; 10-03-2019, 10:03 AM.

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    • #3
      Don't know what your model is as standard but 130mA seems reasonable it would take 384 hours or around 16 days to bring
      the battery down to 50% SOC. Four weeks sitting idle will flatten most newish cars with a few accessories batteries.
      HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

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      • #4
        Originally posted by dBC View Post
        I don't have any current measurements for you, but Is AM2 the main body ECU fuse?
        Yes looking at the Prado 150 wiring diagram it leads to Power Management Control ECU.

        All interior lights were disabled, doors closed and car locked. I have keyless entry so i locked the car and placed the key fob about 10m away (the exterior lights and interior lights come on when i'm about 1.5m near the car if i have the fob on me)

        The measurement was only done for about 1 min after i locked the car so I may have to wait longer to see if sleep mode reduces the current draw. (I'll wait an hour now).


        [Edit] **Battery Saving Function** form the manual
        When entry not used for 5 days or more.
        When the key fob is within 2m of the vehicle for 10 mins or more
        If entry function hasn't been used for 14 days or more
        Last edited by huyjtran; 10-03-2019, 12:48 PM. Reason: Added info from manual

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        • #5
          Originally posted by LeighW View Post
          Don't know what your model is as standard but 130mA seems reasonable it would take 384 hours or around 16 days to bring
          the battery down to 50% SOC. Four weeks sitting idle will flatten most newish cars with a few accessories batteries.
          Thanks for your input LeighW that is reassuring, my google searching was indicating in general half that at ~60mA is normal for most cars with over ~100mA most likely being something shorting or drawing current. My car is completely stock 2010 GXL, no dual batteries. Only electrical additions are a couple of spotties.

          dBC could be onto something - i'll have to check the draw after it enters the various sleep modes.

          If it is not a parasitic current draw, this could mean my battery is dying (less than 6 months old consistent floating charge of 12.5v) or my alternator is not charging sufficiently.

          For the stock alternator, with the car on i'm only getting a reading of up o 12.6-12.7V (maybe 12.8V if I rev above 3500rpm). This again seems low to me and points to a dying alternator.

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          • #6
            Originally posted by huyjtran View Post

            For the stock alternator, with the car on i'm only getting a reading of up o 12.6-12.7V (maybe 12.8V if I rev above 3500rpm). This again seems low to me and points to a dying alternator.
            That definitely sounds like the problem there.

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            • #7
              I f your only getting 12.6V-12.7V your alternator is faulty, first I would check your meter though as 12.6V
              is about what you would get from a fully charged battery. If the alternator is only putting out 12.6V I'm
              surprised your getting any charge into the battery.

              Standby current varies from car model to car model, ECU will draw some current for standby power, as will the instrument
              cluster and car radio etc. I have a CB, HF and VHF radios connected to the aux, standby current is over 100mA.
              HKB Electronics, manufacturer of the Alternator Voltage Booster, Silver 2008 D4D,Lifted,Underbody protection, Alternator Voltage Booster, Tiger Z winch, Lightforce DL, Air Horns, Tanami Drawers, Drop down fridge slide, Outback cargo barriers, Rotronics dual Battery system, Polaris GPS, HF/UHF/VHF, Radio speaker combiner, Long ranger water tank, Diff breathers, Inverter, Snorkel and others

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              • #8
                Thanks for the advice all. Root cause was a dying alternator, intermitently outputting power to charge the battery. It was still outputting enough power that the dash light did not come on. Replaced the alternator and now getting consistent mid 13.5v at idle.

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