Disconnecting battery on car - computer problems?

[Daffy D]

Cars these days have lots of electronics and are almost run by computer, so is there any problem with disconnecting the battery? Will the system have to be re-set or re-booted?

Also long time ago I read somewhere that special care had to be taken when jump starting on new cars as the electronics could be damaged. Any truth in that?

As you might guess I'm from the "old days" where stuff under the bonnet was recognizable

Cheers

[hansnl]

As I know from driving one of those electronic wonders where even the throttle was governed "by wire", I am very careful to disconnect the battery, and jumo starting is a big no-no.

If a new battery is necessary, I connect a small battery to the clamps, and then disconnect and connect the main battery.

Jump starting, I am sorry never had to resort to that.

However, I have an idea this might not be a problem, there is no hiatus, just a supply from another battery.

But as I am also, I presume like you, somewhat archaic, I could be wrong about the jump starting.

I do know from my son, who is in the car repair business, bridging the electric supply when changing the battery is a good idea.

I do remember that Landrover Defender advised to not to disconnect the battery withoud bridging the supply.

Something to do with the security system.

[Gsxrnz]

RTFM

[mogandave]

Anything that truly requires back-up, should already have a separate battery to back it up.

I know Isuzu always disconnects the battery when they service the car, and I think that is pretty is typical.

As far as jumping a car off, the safest way to do this is to leave the key off in the dead car, connect the cables positive first, negative last. When you connect the negative, you should hear the alternator kick-in and the engine load-up on the car that is running. Idle it up a little and let it run and charge for a few minutes. Disconnect the negative cable and try to start the dead car. If starts great. If it tries to start, but does not quite have enough juice, reconnect the negative and repat the charging process a little longer.

Please note that the above is for a negative ground vehicle. If your vehicle is positive ground, connect the negative first. Regardless, always connect positive to positive and negative to negative.

[VocalNeal]

[WarpSpeed]

Most electronic systems these days in order to reboot from problems or to wipe faults from them REQUIRE disconnecting the battery, they also have over-load protection which protects and reboots in the event of an overload say while jumping for example (which doesn't happen all that often BTW as it's governed by both electrical systems on both vehicles) the exception would be of course if someone was stupid enough to cross polarities while hooking up the jumpers which is bad in any case, but more so the explosion risk. So in that case the remedy would be a battery disconnect and reboot.

Cautions by manufacturers are for the most part disclaimers for their own purposes and not true across the board with trained technicians, only novice vehicle owners who need to pose these questions on the Internet, that's not intended to be a dig but merely a fact. Therefore jumping is NOT a no-no for everyone, just unfamiliar novice owners.

Even if memory is lost it is more an inconvenience then necessity in most cases as they are easily reprogrammed but the above pictured external power source is one option to prevent the loss of programming.

[Daffy D]

Thanks for all the replies.

So there is no problem with disconnecting the battery. But would settings in say "Navigator" be lost?

Not sure if the plug-in suggested by "VocalNeal" is viable. I can see the principle but wonder if 9v would be enough to save the memory but guess that unless the key is in at least the accessory position it would not work anyway.

I can see that jumping from a spare battery should not be a problem but what about jumping from another car where you have two sets of electronics that maybe don't like each other?

"WarpSpeed" Appreciate you comments, sure one could go out and just "Do it" and before the Internet I guess many did that and learned the hard way. But now posting questions, even if one knows the answer just to get confirmation, costs nothing and keeps notice boards like this alive.

Have a nice day

[VocalNeal]

costs nothing

It does it costs my time and the time of anyone who responded.

[fredob43]

costs nothing

It does it costs my time and the time of anyone who responded.

Well you know the answer then don't respond.

Genuine question for some one who doesn't know about these thing's I had a Ford in England some years ago and a dead battery caused no end of problems. Now own a Fortuner and if the battery has to be changed my Auto window,s will not work for 24 hours until it reset's it's self, like wise the S/N has to be reset but that's easy by just touching the on screen reset button. As for any other bit's they all seem to work ok.

[Kwasaki]

Thanks for all the replies.

So there is no problem with disconnecting the battery. But would settings in say "Navigator" be lost?

Not sure if the plug-in suggested by "VocalNeal" is viable. I can see the principle but wonder if 9v would be enough to save the memory but guess that unless the key is in at least the accessory position it would not work anyway.

I can see that jumping from a spare battery should not be a problem but what about jumping from another car where you have two sets of electronics that maybe don't like each other?

"WarpSpeed" Appreciate you comments, sure one could go out and just "Do it" and before the Internet I guess many did that and learned the hard way. But now posting questions, even if one knows the answer just to get confirmation, costs nothing and keeps notice boards like this alive.

Have a nice day

On some cars disconnection of battery will put the car on say ! " A safe mode " until you get to a dealer who will reset the ECU for you in a short time, usually no problem, happened to me with my wife's Yaris.

I don't know all the cars that it applies too but when the battery goes dead you don't have much choice, jumping from another car is no problem at all as long as the obvious poles of battery connections are the same of course.

[Tywais]

When I had to change the battery on my Civic, 3 things were affected:

1. Car radio clock had to be reset, minor thing but not straight forward and had to look it up in the manual.

2. The auto up/down for the driver side window stopped working and was manual only. That is I had to hold the button to move it into full open/closed position. Was sure something broke. Nothing in the manual and had to dig around Google to find the answer.

3. The auto locking system. It has 3 modes - 1 is manual lock/unlock only, 2 is by gear position and 3, my preference, is by car speed. It auto locks the doors at 15kph and unlocks when gear put into Park.

[Daffy D]

Tywais - I can understand having to set the clock but did everything start to work again by it's self eventually?

A previous poster said his auto windows did not work for 24 hours till the reset themselves.

Hopefully with a fairly new car these problems will not arise but good to know these things.

[Tywais]

Tywais - I can understand having to set the clock but did everything start to work again by it's self eventually?

A previous poster said his auto windows did not work for 24 hours till the reset themselves.

Hopefully with a fairly new car these problems will not arise but good to know these things.

I had to reprogram them manually by rather convoluted switch pushes and hold and counting seconds to get them back. The windows took me several days to get it fixed as I had difficulty locating the programming information so no auto reset on them. It is a fairly new car and everything else, especially critical items like the key codes or ECT there were no problems. The car is fairly new 2010 model.

[kotsak]

When I had my battery replaced the engineer did it with the engine running, no issues afterwards :>

[Daffy D]

When I had my battery replaced the engineer did it with the engine running, no issues afterwards :>

I thought you shouldn't do that with an alternator.

I know in the "Good Old Days" when cars had dynamos it was OK, but then there were no electronics to worry about

[Kwasaki]

Tywais - I can understand having to set the clock but did everything start to work again by it's self eventually?

A previous poster said his auto windows did not work for 24 hours till the reset themselves.

Hopefully with a fairly new car these problems will not arise but good to know these things.

I had to reprogram them manually by rather convoluted switch pushes and hold and counting seconds to get them back. The windows took me several days to get it fixed as I had difficulty locating the programming information so no auto reset on them. It is a fairly new car and everything else, especially critical items like the key codes or ECT there were no problems. The car is fairly new 2010 model.

Did reprogram the ECU fueling as well to see whether it was correct.

[Tywais]

Tywais - I can understand having to set the clock but did everything start to work again by it's self eventually?

A previous poster said his auto windows did not work for 24 hours till the reset themselves.

Hopefully with a fairly new car these problems will not arise but good to know these things.

I had to reprogram them manually by rather convoluted switch pushes and hold and counting seconds to get them back. The windows took me several days to get it fixed as I had difficulty locating the programming information so no auto reset on them. It is a fairly new car and everything else, especially critical items like the key codes or ECT there were no problems. The car is fairly new 2010 model.

Did reprogram the ECU fueling as well to see whether it was correct.

I noticed my fuel usage had gotten worse by about 10% and may have started around that time. I've always used 91 benzine but had to switch to 91 gasohol which should be no more than a 3% change. Since have tried 91 benzine again, 95 gasohol and 91 gasohol and all 3 around the same 10% higher usage. Will have that looked at.

[transam]

When I had my battery replaced the engineer did it with the engine running, no issues afterwards :>

Yep, done that too in the past with alternator rides .

[WarpSpeed]

Scary stuff though.