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New method of parasitic draw testing leads to diagnosis of battery-killing Honda

Monday, September 2, 2019 - 06:00
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While employed as a sales representative for a diagnostic tool manufacturer, I remember coming across a particular gentleman to whom I was trying to express how important it was for us to keep changing along with the vehicle technology confronting us. If I recall, he went by the nickname “Cooter” (hi Sam!). In a way that I thought he would comprehend, I strived to express how doing things the old-fashioned way on modern vehicles simply doesn't work. I mentioned computer-controlled alternators and then he interrupted me.

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Vehicle Information: 2015 Honda Civic Si
Engine:  Rice Burner 2.0L L4 DOHC
Trans.: Manual, 5-Speed
VIN:  2HGFG4A57FH704743

He took offense to what (I believed at the time) was an educational opportunity, and let me know with a reply of "Are you calling me stupid? You think I AM stupid, don’t you? I've been doing it this way all my life! I don't need to be spending my hard-earned money on your high-priced equipment!”

Of course after that there was no point in continuing to convince him that sometimes employing the old fashioned ways may not be a wise choice and they may actually cause more problems than they solve. There was simply nothing I could say to “Cooter” that would help him understand he could improve the way he was diagnosing vehicles or to get him to consider other ways that would accurately and efficiently diagnose today’s vehicles.

As I was leaving his shop, I remember him trying to tell me that “no equipment could tell (him) the alternator was faulty any better than” the method he uses. He said if he “disconnected the battery cable while the engine was running then he’d know one way or the other.” Yes, I cringed when I heard that.  Hopefully, you did too when reading it.

What would you do if someone told you there's an easier, more efficient way to do something that you have done the same way for a long time with excellent results? I’d say “prove it!” In most cases there's no reason to change the way we are doing things as long as they work and provide us accurate information. There are circumstances however, that make you have to change — maybe against your will!

It really doesn't matter what brand of vehicle you are working on when you are trying to address a "parasitic drain" (also called a “parasitic draw” or just a “draw”). The problem is usually that the vehicle’s battery has gone dead with no reason, within an unreasonable amount of time.

This may be that day!

In the “old days,” to diagnose a parasitic draw — on a vehicle with the key off — we would disconnect a battery cable and put a non-powered test light in “series” or in other words, between the cable end and the battery terminal. If the light lit, we knew we had a draw. If the light didn't, either the problem was intermittently occurring or we knew that something was probably left on and has now been turned off.  Once sure there was a draw, we would disconnect one fuse at a time until the test light didn’t shine anymore. A long time ago the fuse blocks were fairly simple and usually identified the whole circuit each fuse protected so we knew which system was affected and would start working towards the component at fault – isolating items that fuse fed.

Sometimes there are more tools than engine in the engine compartment!

After electrical systems became more complex it became imperative we had to have accurate service information that included electrical wiring diagrams. With the advent of “Maxi” fuses providing many smaller fuses with protection then came the time when multiple circuits could be protected by one larger-capacity fuse. We would begin the tests the same way (test light attached at the battery), but then we’d disconnect the high amperage rated fuses one at a time. Once we identified which of the higher amperage fuses were carrying the parasitic load (draw) then we’d pull those lower amperage fuses that were protected by it one at a time.

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