There is a YouTube channel that has a lot of excellent content on finding and fixing parasitic electrical draws. Pine Hollow Auto Diagnostics.
nb: I am not affiliated with this chan, just a fan.
I fixed a parasitic drain on my car in 408 days
51–60 of 515 posts
Re: I fixed a parasitic drain on my car in 408 days
#52Well this is timely. I have a parasitic draw on my NC Miata. The first mechanic just replaced the battery. The second told me it's normal for the battery to die if you don't drive it for 3 days (because "cars have computers now"). It seems like mechanics really don't like digging into the electrical part of the car... but these days that encompasses more and more of what can go wrong. Without time to dig into it myse…
Don't ever go back to that second mechanic.
Re: I fixed a parasitic drain on my car in 408 days
#53Intermittent car issues are the worst! Related is the 'My car hates vanilla ice cream' story: https://web.archive.org/web/20060213052358/http://www.campbe...
Maybe I've read this before, but I guessed by the problem description that the answer probably had something to do with time...
Re: I fixed a parasitic drain on my car in 408 days
#54Earlier quoted context omitted.
It's fairly straightforward if the car is unmodified, as everything should be fused. Multi-meter between positive terminal and positive lead and pulling each fuse to see when the drop goes away will isolate the circuit. Then you've narrowed it down pretty far and can go from there. The horrible thing is if the car is modified, and you discover an un-fused circuit.
> Ammeter across the battery terminals I know what you're trying to say... but this reads like very dangerous advice and you may want to revise. Ammeter between a battery's terminal and the car's electrical system. Also note that you'll probably create sparking when doing this, and if the battery has recently been charging this can be dangerous (hydrogen outgassing).
I think the mistake may have actually been writing ammeter instead of voltmeter. Ammeter is not safe as general advice as a typical one won’t be anywhere near large enough capacity for working with a car battery and should come with a lot of disclaimers about how to hook it up. Measuring voltage drop would work but only for fairly high loads.
Re: I fixed a parasitic drain on my car in 408 days
#55Earlier quoted context omitted.
> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit.…
Probably should get a brand more reliable than Audi...
I hear people say that about my BMW, and realistically the hassle of some reliability issues is nothing compared to driving the lifeless husks of cars they recommend instead.
(there are reliable sports cars, but it significantly limits the pool you can select from)
Re: I fixed a parasitic drain on my car in 408 days
#56I used to be a computer engineer working on embedded systems for automobiles. Quiescent current is what the normal proper draw is called for these systems when the car is off. We worked very hard getting these numbers in spec but it was hard to catch everything especially in this case where the issue is probably due to software missing the sleep state for that module. This could be from bad code or your CAN/LIN bus i…
> This could be from bad code or your CAN/LIN bus is messed up in your car.
If the car had been operational for years and years, why would bad code crop its head now?
Re: I fixed a parasitic drain on my car in 408 days
#57Earlier quoted context omitted.
> It seems like mechanics really don't like digging into the electrical part of the car... Tell me about it. I'm in a similar boat. My audi a4 has had a parasitic draw for the past 10 years. My mechanic didn't want to take the time to address it because that sort of thing takes a serious amount of time and he's always backed up. I got out my fluke and narrowed the cause to what I believe is the comfort control unit.…
Probably should get a brand more reliable than Audi...
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Re: I fixed a parasitic drain on my car in 408 days
#58Is it possible the key fob just needs replacement and is causing the intermittent sleep failure?
I was also curious about this. Maybe the keyless entry computer stays awake to try to sync with a fob and then sleeps on success? If a user chooses not to use a fob at all, maybe it stays awake indefinitely trying to find a key to sync with.
From my own experience I believe the issue is that when these modules start to go bad they fail to turn off and stay awake indefinitely.
Re: I fixed a parasitic drain on my car in 408 days
#59Earlier quoted context omitted.
> Ammeter across the battery terminals I know what you're trying to say... but this reads like very dangerous advice and you may want to revise. Ammeter between a battery's terminal and the car's electrical system. Also note that you'll probably create sparking when doing this, and if the battery has recently been charging this can be dangerous (hydrogen outgassing).
I think the mistake may have actually been writing ammeter instead of voltmeter. Ammeter is not safe as general advice as a typical one won’t be anywhere near large enough capacity for working with a car battery and should come with a lot of disclaimers about how to hook it up. Measuring voltage drop would work but only for fairly high loads.
> Measuring voltage drop would work but only for fairly high loads.
Yah, that doesn't really make sense for small parasitic loads.
> Ammeter is not safe as general advice as a typical one won’t be anywhere near large enough capacity for working with a car battery
It should be fine with the car not "on", but the general level of danger of doing anything near a car battery requires caution.
Re: I fixed a parasitic drain on my car in 408 days
#60I have failed to find the parasitic draw on an RV (slower than this one, it takes a couple weeks to kill the battery). I finally got a "Top Post Battery Master Disconnect Switch", which is a little dinglebob that goes between the battery post and cable and lets you easily break the circuit. I highly recommend the $12 solution for an intermittently used vehicle.
I thought about this but the problem with newer cars (mine at least) is killing the power wipes the memory so it won't pass an emissions check (or something like that). After my battery died I had to find an excuse to drive an extra 100 miles so I could pass emissions. On my car the emissions laws definitely caused more emissions than they saved that day.
I once had a car where I had to disconnect the battery to clear the check-engine light so it would pass a state inspection.