What a batteryless car 'remembers'

[JuanTwoThree]

The total miles/kilometres that my car has done appears on a tiny screen where the time and date, range, trip distance and other stuff also appear:



If the battery goes flat or is disconnected completely for a time then it forgets what year it is, the time, date, how you drive and so on. But the one thing it doesn't forget is how far the car has been driven in its life. I suppose it's like what a computer remembers as ROM when it's off. But why doesn't it remember a bit more? I had to reset absolutely everything and reteach the car how I drove because the car had been sitting there for months and the battery had gone flat.

Also, how easy would it be to reset the distance on a digital odometer? Not that I would! Just curious.

 

[existentialist]

The total miles/kilometres that my car has done appears on a tiny screen where the time and date, range, trip distance and other stuff also appear:

View attachment 232821

If the battery goes flat or is disconnected completely for a time then it forgets what year it is, the time, date, how you drive and so on. But the one thing it doesn't forget is how far the car has been driven in its life. I suppose it's like what a computer remembers as ROM when it's off. But why doesn't it remember a bit more? I had to reset absolutely everything and reteach the car how I drove because the car had been sitting there for months and the battery had gone flat.

Also, how easy would it be to reset the distance on a digital odometer? Not that I would! Just curious.

It's EEPROM or flash memory, which is rewriteable, but maintains its state without power.

I think digital odometers are supposed to be pretty difficult to cheat...but I wouldn't be at all surprised if there isn't some kind of back door, accidental or otherwise.

It's doable, but apparently involves soldering of SMD devices. Fuck that.

DIY: Odometer Reprogramming

DIY: Odometer Reprogramming: Here’s how to reprogram your odometer after an instrumentcluster swap. The vehicle this was demonstrated on is a 2004 Honda Accord. YouTube Video: DIY Honda Odometer Reprogramming https://www.youtube.com/watch?v=NmyERHeDlTw Disclaimer: 1. The…

www.instructables.com

 

[mauvais]

The mileage is typically stored in various different control units.

This may no longer be the case but in the past - 90s and 00s - if you replaced the speedometer it would replace the shown mileage, although a correct reading would remain in the ECU. I think some places could adjust it.

As for why not everything is retained when power is lost, same thing, held in different modules and they don't necessarily need persistent memory.

 

[JuanTwoThree]

My 2008 car thinks it's 2006 after the battery is reconnected. Do newer cars have more information saved in that EEPROM than just the mileage? It seems a waste not to give it more to do.

 

[mauvais]

I don't know, I imagine newer cars have something more like a proper operating system and retain a lot more data, but it will vary based on the complexity. Remember also that EEPROM has advanced over time. It used to be pretty rare and no doubt expensive. It also still needs power - even SSDs will lose their data if unpowered for a few years.

 

[DownwardDog]

My 2008 car thinks it's 2006 after the battery is reconnected. Do newer cars have more information saved in that EEPROM than just the mileage? It seems a waste not to give it more to do.

My wife's BMW uploads all its data to the BMW cloud so even if you disconnect the battery, wipe the NVRAM, etc. it'll just restore itself when everything is powered up and it connects to the Internet again.

 

[WouldBe]

It's EEPROM or flash memory, which is rewriteable, but maintains its state without power.

I think digital odometers are supposed to be pretty difficult to cheat...but I wouldn't be at all surprised if there isn't some kind of back door, accidental or otherwise.

It's doable, but apparently involves soldering of SMD devices. Fuck that.

DIY: Odometer Reprogramming

DIY: Odometer Reprogramming: Here’s how to reprogram your odometer after an instrumentcluster swap. The vehicle this was demonstrated on is a 2004 Honda Accord. YouTube Video: DIY Honda Odometer Reprogramming https://www.youtube.com/watch?v=NmyERHeDlTw Disclaimer: 1. The…

www.instructables.com

Don't see why you can't program the eeprom in situ as the car has to do it each time you drive another km.

 

[WouldBe]

As for why not everything is retained when power is lost, same thing, held in different modules and they don't necessarily need persistent memory.

Clock requires pulses from an oscillator to keep the time which requires power. Although with modern tech I don't see why the clock can't update itself from a radio frequency clock or from the net so it's always correct.

 

[Saul Goodman]

Don't see why you can't program the eeprom in situ as the car has to do it each time you drive another km.

You can. You must need the right tools, and a lot of cars store the mileage in the ECU now.