OT Car Battery Replacement

Assuming "ECU" means the emission control monitors or engine computer, there are no security codes for it. Some cars might have a security code for the radio, the owner's manual would cover that. I can tell you the BMW x5 here, there are no codes. After a loss of power, only the date and time need to be set.

But how many of those get lost when power is interrupted, then restored?

THAT *is* "a" _very_ GOOD (question) --- "I" am GLAD *you* _asked_ IT!

It only has to happen ONCE if it happens to you. Once is too often.

Exactly. A car isn't like a PC -- there are LOTS of little processors scattered around the vehicle. Often, designed by different groups and pieced together. Legacy systems being used in places where a complete redesign wasn't considered necessary.

Does each little box keep it's own settings? Do they expect some "master" to provide "configuration data" that they can use? When? each time the ignition is switched on? Each time a door is opened? Each time "fresh power" is sensed?

El cheapo microcontrollers may have very tiny amounts of nonvolatile memory -- often with strict limits on how often it can be erased/rewritten. So, while the controller that draws all those pretty graphics on the screen for you may have significant horsepower, the one that remembers your mirror position may be a real dog!

Wanna bet even the dealer doesn't know the fine details? ("Which version of the software are you running...?")

Virtually none of the settings are easy to re-set. You have to scan for stations to *find* those that can be received in your current locale -- for AM, FM and XM. Then, have to decide which of those you want to save as your presets. Your spouse has to repeat the exercise.

If any of your presets are from your "vacation home" or out-of-town workplace, you can't set them until you are AT those locations.

Readjusting seat and mirrors takes time -- plus telling the car to "store" those settings.

Typing in the names of each GPS "destination" using a touchscreen keypad. "Hmmm... what's Bob's address? I can't seem to SEARCH for 'Bobs House'..." Do you even remember what all of the destinations were?

Drag out each of your cell phones and pair them with the vehicle. Any BlueTooth headsets? Transfer your telephone books to the vehicle.

Plus all of the "optional configuration" stuff. "Hmmm... did I have the autoheadlight sensitivity set to LOW? Or MED?"

And will you remember that you want the "Auto Door Unlock" setting to be "Off" instead of the default "All Doors When Driver's Door Opens"? (Because the default would allow someone standing by your passenger door in a secluded parking lot to let himself into your vehicle despite the fact that you are rushing to gain the security of that vehicle for JUST yourself!) Yet, you want the "Key and Remote Unlock Mode" to be "All Doors" instead of the default "Driver Door" (think about it)

Do you even remember the procedure to set each of these? Or, will you be scrambling to paw through 500+ pages of "owner's manual" hoping to track down each setting's explanation and method of setting?? Or, pestering the dealer for help?

That's what it should be like. Memory that can hold its contents during a power outage has been around a long time.

If your car/truck has OBD-II, the ECM will need to "relearn" it's operating characteristics. In other words, don't go out and try to "smog" it anytime soon

On Fri, 04 Mar 2016 17:36:34 -0500, snipped-for-privacy@snyder.on.ca wrote in

snip

Something I just thought of: On newer model cars, the cig lighter receptacle is "off" unless the car is in the "on" or "accessory" key position. ISTM that if the cig lighter receptacle of "off", none of those charger or memory devices will work. Is that correct?

Current "memory that can hold its contents during a power outage" is FLASH (in ages past, there was core, bubble, BBSRAM, MNOS, etc.). FLASH has limited write cycle performance -- you can't read and write it "casually"; it "wears out".

Additionally, writing FLASH takes a LONG time (in terms of CPU time -- like thousands of times slower than writing to RAM). And, you must have recovery algorithms in place in case the write

So, using FLASH means a more involved data retention strategy:

- keep "working" copies of all data in (volatile) RAM

- periodically (when?) flush those values to FLASH (for safe keeping)

- if the working copies are "suspect", reload them from FLASH

- verify the integrity of data stored and retrieved to/from FLASH (e.g., checksums)

Deciding when to move things into/out of FLASH becomes a separate design challenge; what if two values are related to each other in some way? Then, you must ensure you move BOTH of them into (or OUT OF) FLASH at the same time. Otherwise, you risk the system getting confused (inconsistent state).

Then, you have to decide *where* the data will reside, physically. Which of the 10, 20, 30 little "smart boxes" (CAN nodes) scattered around the vehicle will hold each datum? And, as those boxes can be replaced, over time, how do you ensure the data they contain remain pertinent? Or, are automatically invalidated ("Hey, this isn't the same car that I was in last time I was powered up!")

OTOH, just letting all of the data sit where it would NATURALLY want to sit -- in RAM (which is actually BBSRAM -- "Battery Backed"!) eliminates a lot of these issues.

Take the disk drive out of your PC and you remove an entire layer of software from it!

Yes. So, you have to put the car in ACCessory mode. As I mentioned upthread, in our vehicle, that turns on all sorts of things (digital dash, navigation system, etc.). So, you're suddenly powering more than JUST the "settings memory".

A 9V battery sourcing tens of milliamps will last hours. That same battery at an amp would last ~5 minutes. And, that assumes its a "fresh" battery -- and, not one made in People's Really Good Battery Factory #773.

Additionally, there's some concern over how power is switched/gated to that outlet. Is it a mechanical switch (relay)? Or, a solid state device (FET)? Did the circuit designers expect current to flow *in* through the "lighter" socket?

Irrelevant because those microcontrollers don't have individual security codes. Off to the wilderness again.

Taken car of by the car manufacturer.

Irrelevant

The dealer doesn't know the fine details because they don't need to. How to enter a security code for the radio, or some master security code for the theft deterrent system, that they would know.

Yawn. Maybe on you're car. Last IDK how many cars I've owned, the radio remembered the presets when power was lost. After all, the non volatile memory necessary to do that costs about 10 cents. The only thing I have to enter on the BMW X5 is the date and time.

Show us the car example where all that is lost when power is interrupted. And I'll show you a car company with no customers.

Apparently there are some here that don't think so. Not only has that memory been around for a long time, the cost of it to hold some trivial settings is probably 10 cents. Let's see, spend 10 cents on a few bytes of memory or have inconvenienced, pissed off customers? What would Jesus do?

Bad example too. The PC is like a car. There is a microcontroller in the disk drive, in the optical drive, probably in the wireless mouse, the audio card, video processor in the video card, etc.

If it's off, then it's not going to work. I think many cars though still have cig lighters that are on all the time, because people want to use them to charge phones, etc while they may be away from the car. You could still hook one of the devices to the car another way, like at a jump start terminal, if it has one under the hood, etc.

On some cars.ome have 2 "accessory outlets" - one live and one switched. Some have more than 2, with at least one "live"

Not aware of any vehicle that will not accept pwer in - not aware of any vehicle where the "accessory outlet" (the device formerly known as a cigar or cigarette lighter) is switched by anything fancy. - but that doesn't mean they don't exist. - and more and more vehicles have a non-switched "accessory outlet" somewhere in the vehicle.

Dunno. I haven't designed any automotive electronics for a decade. But, back then, there was a growing concern for using "smarts" to replace *wire*, moving to 48V systems, etc.

There are two "Power Outlet"s in our vehicle. Both are switched (and, may, in fact, share the same 15A fuse!)

I've not yet purchased a shop manual so I can't tell, for sure, how things are wired.

But, if *I* have to swap a battery, I'll drag out a lab supply, program it for 12.0V, set the current limit to a few amps (to be safe) and jumper to the battery cables (I'm not sure if anything would get upset if I connected to the frame instead of battery minus -- as *something* is watching current OUT of the battery...)

The frame and the battery cable to the starter or alternator will both work - which ever is easiest to get to.

Shade Tree Guy posted for all of us...

I didn't count all the replies but if one assigns a $1 to each one then he could have a new battery installed by the dealer for less. He seems to have a higher end model but wants to cheap out on maintenance. Over & out.