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How do I find a parasitic draw?

Discussion in 'Audio & Electronics' started by doncaruana, Mar 7, 2020.

  1. doncaruana

    doncaruana Member

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    My 97 Tahoe has a parasitic draw on it somewhere that will kill the battery after about 5 days. I can afford to let it sit now so I can do whatever I need to find the draw. But how do I find it?
     
  2. PNW VietVet

    PNW VietVet Supporting Member

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    Make sure battery is fully charged. Plus, 5 days is a long time for it to drain a battery. Are you saying that if you tested the battery after 5 days it shows no voltage? Or are you saying if you let it sit for 4 days the engine would start? Have you monitored the battery over the 5 days to see how much voltage it is losing?

    Attach a digital multi meter between the battery negative and the end of the negative cable. Set the meter to read milliamps. Keep in mind that you have "keep alive" draws on your rig. Computer memory, radio clock....etc, so you should see some milliamp draw when you hook up. If the battery is not fully charged during this process, it should be.

    I know on newer rigs there is a larger milliamp draw than what I used to see when I was in my shops. I used to use 50 milliamps as a threshold. I would say your 97 Tahoe qualifies as an older rig. Anything over was not good. If you are over that start taking fuses out one at a time and when you see the higher milliamp draw go away then the work begins. You need to find out what components are on that fuse circuit and start disabling them one at a time to find the culprit. There may be only one component on that fuse or multiple items. The first thing I always did before I even started pulling fuse was unplug the alternator to see if the draw disappeared. Usually easy to get to and was a culprit many times. It could be simple or difficult but the initial set up, as I explained, is to get you ready to diagnose.

    Others here will chime in.
     
  3. doncaruana

    doncaruana Member

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    If it sits for 5 days or so, the battery will be dead enough to not start. Although, having said that, I just started it after 5 days and it cranked right up - this time at least. I recently replaced the ac/heat control panel which may have been doing that (it died in glorious fashion one night with the smell of burnt plastic and smoke rolling out of the dashboard!).

    My other issue of course is that at some point, someone (me??) used the wrong side wrench on the negative terminal, so it's not easy to get off (I have on my "to do" to replace that). Could I put the meter on the positive terminal instead?
     
  4. PNW VietVet

    PNW VietVet Supporting Member

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    No, should be negative terminal. Go to the parts store and get a new cable end nut for GM and use a pair of pliers to remove the old nut and yank it out of the plastic shoulder that holds it in the cable end. After what you just said about the battery, how old is the battery, how do you know the battery is a good battery and test the alternator to make sure it is charging correctly. You can take the alternator off and remove battery and have them tested at the parts store if they know what they are doing. Usually Auto Zone does it. Maybe the battery does not hold the charge like it should. Maybe the cable ends are filthy and loose.
     
  5. exp500

    exp500 Full Access Member

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    Hopefully yours isn't an intermittant fault- 96/97 were known for that. Two or three days between use and they lived fine. Some have spent hours searching multiple times. Best time to search is when battery begins to show drop. Don't charge or start it yet or it may "reset". Most draw in 200-300MA range. Hope this helps.
     
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  6. doncaruana

    doncaruana Member

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    Been a long time on this, but eventually I got to where the truck wouldn't start at all. And when I tested the draw, it was only 38ma, then 26, then nothing over the span of about 5 seconds. I started another thread when it wouldn't start (https://www.tahoeyukonforum.com/threads/wont-start-after-a-dead-battery.118882), but the no-start was because of bad battery terminals. I'm wondering if it was also causing the draw. Time will tell...
     

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