Changing a car battery

Probably just a diode. So if someone puts the clips on arse about face it doesn't get fried from the still connected battery and if they proceed and remove the vechicle battery it doesn't fry the electronics with reverse polarity.

Together with wires you don't want to accidentally knock off or short. Think the ciggy socket away from the work area has a lot going for it.

In article , David J scribeth thus

Now how is it when I unplug any PC here it somehow remembers its BOIS memory?..

And they cannot get a car to do this?...

Boggle;!...

Think it's more likely to be some form of interference spike clipper. Like they fit across the battery when doing any arc welding on a car. The giveaway would be if it goes between the leads or is inline on one or both. But they don't seem to list anything like that now.

Deliberate design. It was a method of resetting digital odometers years ago. They now detect this, and some deliberately destroy themselves, rather than risk reporting wrong milage. (Don't know if that's the Jaguar issue, but it sounds like it from that description.)

The usual problems are restricted to the car radio which looses its station memory or and needs re-coding.

Most car radios cost the makers pennies - hence no DAB etc.

My DAB Blaupunkt uses a special SD card for security coding. If you power it down totally, that has to be inserted to make it work again, but it retains all your settings. Once activated you remove that special card and replace it with an ordinary one if you wish to record off the radio, etc.

It's a "security" feature. Just another, small, hoop for tea leaves to jump through.

In article , Dave Plowman (News) scribeth thus

Lets not start that now shall we;!..

I wonder why they bother with it all in modern radios where they are part of the car now, lest the ones I've seen are unlike the standard DIN slot type which are more "pinch-able"..

Ummm .. so the tea leaves will remove or dis the battery and all the info has to be put back in?. Doesn't seem that well thought through to me somehow?..

Surely if the correct coded key isn't used then fine, rubbish or stun the system like we can with some portable radios nowadays but fer christsakes simply swapping the battery;?...

seems harsh - spose must depend on the car - in the past I've changed batts on a '94 XJ6 (and had flat batteries on same) many times without any apparent "damage" save usual radio stuff....

Cheers Jim K

Sadly it's a fact. I'm told 10 dollars is the average cost. So adding a memory back up system could cost quite a bit given the numbers produced. Of course if customers rebelled over having to re-set the radio each time the battery went flat or whatever, the makers might do something. A bit like fitting DAB. ;-) But obviously everyone is perfectly happy...

The Blaupunkt I'm referring to is an aftermarket one. The one in my other car which is definitely fitted to it - it has a double height faceplate - has no coding. But still looses the station memory if powered down totally.

Many engine management ECUs lose important information when powered down - indeed even basic systems often have a recommended sequence for the driver to use after doing so ... usually consisting of allowing the engine to idle for a set time, then holding a set number of revs for further periods, etc. Most *will* re-learn the peculiarities of the engine with normal driving though. I have however heard that one manufacturer's ECUs (I can't remember which) has only limited functionality after reconnecting and must be reset by a dealer before returning to normal.

SteveW

I was in the garage of a large Taxi company near here a few weeks ago and the chief mech there was muttering about the need for yet another PC with all the right software thereon.

Meanwhile another poor cabbie came in to be told that the ECU on his car was naff and thats going to cost him the best part of a grand plus a bit more for programming something that only the dealer could do;!..

Suppose thats progress!...

In article , Dave Plowman (News) scribeth thus

So how come my umpteen year Old Sony can manage OK if un-powered for a while?..

Read an article some time back by a firm who repairs them on exchange, and they reckoned only about half of the ones they get are actually faulty.

I will consider the cigarette lighter approach next time. The three battery technique could go wrong, although I'm used to dealing with large currents (up to 5000 amps even!). I happened to have a spare battery and no cigarette lighter plug. It was nice to not have to reset 27 radio stations and the radio code and the clock.

mmmm nice business for somebody...wonder who pays...

Jim K

If you order up an exchange unit from them, they won't accept it back for a refund unless of course that is found to be faulty. They will however test your own unit for a fee. But since the customer is paying most garages simply fit an exchange unit and get the customer to pay up - even if it wasn't faulty.

I don't see why computers in cars have to be so expensive. Surely the chip costs only a few dollars to make. But mine appears to be controlling the spark plugs and fuel injection etc, i.e. 1000 or more operations per second. A piece of cake for a computer I would have thought.

no s*1t sherlock! ;>))

Jim K