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Comment by JohnFen | Hacker News Reader

I wonder if installing a switch to disconnect the car's battery entirely would be an acceptable (but obviously hacky) solution.

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Not really, When powered down(battery diconnected) the computer then has to re learn parameters/pass internal validity checks. On a well preforming system this will be done in as little 1 or 2 rides but on a marginal system this can take many rides. the computer may not enter closed loop mode until these checks pass.

closed loop mode is where the computer set it's output values(fuel air ratio, timing etc) based on it's input sensors. open loop mode is where it sets it's outputs on known safe working values, but it may not run particularly well. i think this is related to the so called "limp mode"

Note My knowledge on this subject is very out of date. I had to figure it out for my old 2001 car. Newer vehicles may actually have flash storage and the computer parameters survive power out.

Yes, my Audi did not like being disconnected from power. If I remember correctly, it didn't go into limp mode but it was in some partial alarm state when it reconnected such that one had to mimic the Contra cheat code with their fob to get it to shut up. I jest, but yeah. Battery dead was not a condition with a transparent recovery.

Not to mention more minor annoyances like losing radio stations and other settings.

It's insane that this keeps happening. Computers can remember BIOS settings for probably 40+ years now.

But this is usually done on computers with a battery too?

I know.

Yeah, there are lots of ways cars could store such settings that wouldn't be cleared when main battery power is disconnected (which is something that regularly needs to be done when the car is serviced). Flash storage would work too.

They use a battery backup. The main symptom of having a dead cmos battery is that your computer starts loosing it's cmos settings, it's a feature not a bug. I have a system where it keeps the cmos config on flash. the only system I managed to brick(almost). I put a bad config in(never disable usb on a laptop where everything is usb) and there was no easy way to reset it. I had to buy a sioc clip and a chip programmer to reflash the thing the hard way.

The point is all cars have a wonderful battery backup system, and resetting the computer when power is lost is also a nice feature.

I know they use a battery.

it’s a shame that cmos battery technology has remained out of grasp for car radio manufactures these dozens of years

This isn't a good idea for an Audi. The computer doesn't like going without electricity. It runs a bit rough for a day or two afterwards and sometimes will "forget" how much gas is in the tank.

Some newer vehicles get upset when you do that, but older ones generally don't. You may lose radio programming though. I've got an old '95 Caravan that's going to be getting a quick disconnect like this one pretty soon though; the drain takes a few weeks to kill the battery, but we don't drive it very often either. Why do we still own it? With the back seats removed, you can easily put 8'x4' sheets of plywood in it.

I did this with an old vehicle taht was pretty basic without a lot of electronics.

the actual problem was sort of electronic-releated - leave lights on, drain battery to zero.

I put on a battery-cutout-monitor-thing. If battery drained to x%, it would disconnect the battery. to start the car, I think you had to stand on the brake pedal (add a load - like brake lights?) and it would reset and reconnect the battery - then you could start it.

this sounds like the sort of perfectly reasonable system that the original manufacturer could install in order to save the world from buying several hundred thousands replacement car batteries every year.

That would depend on the car brand. Not so good idea in some brands.

Assure to write somewhere your radio code password first.

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