I fixed a parasitic drain on my car in 408 days • Hacker News Board

Re: I fixed a parasitic drain on my car in 408 days

#31

Post by everybodyknows » Mon, Apr 10, 2023, 5:15 PM UTC

rozap wrote: post #9

overthrow wrote: post #3

Well 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…

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 and pulling each fuse to see when the drop goes away

How does this compare with the way presented in the article based on measuring resistive voltage drop across each fuse in turn?

Re: I fixed a parasitic drain on my car in 408 days

#32

Post by mlyle » Mon, Apr 10, 2023, 5:15 PM UTC

rozap wrote: post #9

overthrow wrote: post #3

Well 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…

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).

Re: I fixed a parasitic drain on my car in 408 days

#33

Post by leviathant » Mon, Apr 10, 2023, 5:15 PM UTC

blobbers wrote: post #11

Is it possible the key fob just needs replacement and is causing the intermittent sleep failure?

That's probably what the author was thinking in February 2022 when they removed the batteries from their keyfob and only used the metal backup key, only to have the problem resurface less than a year later. It's probably safe to say that without batteries, the fobs were having no effect on the keyless system housed within the car.

Re: I fixed a parasitic drain on my car in 408 days

#34

Post by localhost » Mon, Apr 10, 2023, 5:16 PM UTC

While not a fix for this problem, a nice form of insurance is a Lithium Ion jump start battery[1]. I'm amazed that a hand-held battery can discharge fast enough to jump start my car, but ... it works great.

[1] https://www.amazon.com/dp/B0B55RFM1Z

Re: I fixed a parasitic drain on my car in 408 days

#35

Post by instaclay » Mon, Apr 10, 2023, 5:18 PM UTC

blobbers wrote: post #11

Is 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.

Re: I fixed a parasitic drain on my car in 408 days

#36

Post by voldacar » Mon, Apr 10, 2023, 5:19 PM UTC

rozap wrote: post #9

overthrow wrote: post #3

Well 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…

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 in series, not across the terminals! Unless you are trying to weld something :]

Re: I fixed a parasitic drain on my car in 408 days

#37

Post by olyjohn » Mon, Apr 10, 2023, 5:20 PM UTC

tadfisher wrote: post #26

kccqzy wrote: post #7

Earlier quoted context omitted.

> it's normal for the battery to die if you don't drive it for 3 days I've heard this nonsense a couple times now. I was incredulous at first but everyone seems to say this. What are anyone's suggestions for a weekend-only car? (I bike to work so I don't need a car on weekdays.) Trickle charge the car battery on weekdays?

You can drive a car from the 90s before they started shipping alarms and keyfobs in every vehicle. My 1995 Miata draws just enough power to maintain the clock in the radio, and it starts just fine after sitting for 6 months (it's not a winter car).

My 2000 Ford Explorer has all kinds of electronics and modules from the factory. And even my crap I added in... I leave my Qi charger, ham radio, Bluetooth FM transmitter all running and plugged in, and I can come out a week later and the battery is still not dead. And when I'm camping I run a 12v van all night long. Truck starts right up every time. I don't get what would be draining more power than that in a more modern car. You'd think they'd be more efficient at not wasting juice.

Re: I fixed a parasitic drain on my car in 408 days

#38

Post by addisonl » Mon, Apr 10, 2023, 5:20 PM UTC

lylejantzi3rd wrote: post #28

overthrow wrote: post #3

Well 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…

> 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...

Re: I fixed a parasitic drain on my car in 408 days

#39

Post by FartyMcFarter » Mon, Apr 10, 2023, 5:21 PM UTC

kccqzy wrote: post #7

overthrow wrote: post #3

Well 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…

> it's normal for the battery to die if you don't drive it for 3 days I've heard this nonsense a couple times now. I was incredulous at first but everyone seems to say this. What are anyone's suggestions for a weekend-only car? (I bike to work so I don't need a car on weekdays.) Trickle charge the car battery on weekdays?

I didn't drive my 2019 Mercedes for months during the pandemic and the battery was fine. It did give me a warning when I restarted driving it (I guess the battery was starting to get low-ish), but it immediately fixed itself.

Re: I fixed a parasitic drain on my car in 408 days

#40

Post by ceautery » Mon, Apr 10, 2023, 5:22 PM UTC

This is type of thing I've seen Eric O. over at South Main Auto[1] fix in dozens of videos. Mad troubleshooting skills, works hard to find root causes of things. He's pretty amazing, hidden away in some no-account town in upstate NY.

1 - https://www.youtube.com/@SouthMainAuto