Removing the battery from a modern car? - chas
As most modern cars have electronic management systems , are there any safeguards required when disconnecting/changing the car battery.

I know about the Radio Security code but wondered if these management systems also "lost" their memory on disconnection of the battery supply for a long period of time ?

I`ve been "told " , that on Fords , the engine management system "recalibrates" itself over the next 10 miles.

Is this true and if so , how does it do that ?


Removing the battery from a modern car? - Dave N
On many of the latest cars, disconnecting the battery can be fatal. Take the example of my girlfriends new Seat Ibiza. It's been in the garage for a week as they can't code the keys back in to the ecu after disconnecting the battery and replacing the instrument cluster. Even the a/c compressor needs coding on some of the latest VAG cars after replacement. As an example of how everything needs to speak to each other, the fuel pump starts up when the doors are opened, meaning there is a link between the interior lights and the ecu, umbelievable. It all means that disconnection of virtually anything, including the battery, can disrupt the communication between all the various electronics, and the physical reconnection doesn't necessarily mean an electrical connection recognised. The same can apply to a totally flat battery.

On the last of the old shape Range Rovers, the keys also need to be coded in on disconnection of the battery in order to stop the alarm going.
Removing the battery from a modern car? - Micky
And this is progress?
Removing the battery from a modern car? - jaapie
Ok so i have read all the posts here,but can i ask about a VW Polo 1997 1.6L Auto,does anyone know about the results if changing its battery,i know that the Radio will have to be reset,but what about the rest of the memory of the ECU?? WILL THIS STILL BE ok??
As the VW isnt mentioned at these posts i hope there is someone who really knows about them.
Thanks in advance.
PS: i want to recharge the battery so it will be out of the car for a few hours.
Removing the battery from a modern car? - sean

I believe that I have already answered this for you.

The right answer.

If I have not, please write back, as I have now enabled e-mail notification below.

The precis is "no problem" wink, wink.
Removing the battery from a modern car? - jaapie
Hi there Sean,
Thanks for the reply,yes all went well i recharged the Battery and then replaced it in the correct order,it started first go and all i had to do is reset the Radio Stations which was a Breeze!
Thanks again.
Removing the battery from a modern car? - John Davis
Could anyone advise please? With all this complexity, on modern vehicles, and the possible "fatal" consequences of disconnecting the battery, are these plug in devices, ie, into the cigar lighter/power socket, which, I understand "grabs" all the pertinent information, any good ? Can you still come unstuck with messed up codes etc even if you use one of these devices ?
Removing the battery from a modern car? - jc
The plug-in in the lighter socket doesn't grab anything-it merely keeps a voltage on the car systems to avoid losing the radio code.On a Ford;you can feed the radio code back in in less than a minute,you won't affect the keys and the ECU will do it's "fine-tuning" of the calibration in less than ten minutes of idling and driving.
Removing the battery from a modern car? - lezebre
The world is changing so fast it's leaving most of us behind.
But don't worry, your Ford ka, sorry, car, will keep up with all the technology, but most important of all, it won't bite.

If any ad agency picks this up, could they cut jc and me in, please?
Removing the battery from a modern car? - T Lucas
Sounds like a good reason not to own a Seat Ibiza.
Removing the battery from a modern car? - pastyman
Removing the battery from a modern car? - Mondaywoe
Interestingly..... My Citroen C5 (positively dripping with electronics, computers etc) had a problem with the electric windows - the front ones wouldn't close. I phoned the dealer, expecting major fault-finding operations, computer diagnostics and probably no real solution at the end of the day!

'Disconnect the battery for 10 seconds' they said.

'Are you sure? Won't it wipe all the ECU info, suspension software etc etc?'


Bit of a dilemma really! Did the Citroen Dealer really know about Citroens? (Don't laugh!) or was he just trying to fob me off? Bearing in mind he is listed in the Honestjohn list of top garages (rightly so BTW), I decided to trust him and try it

The car sorted itself beautifully (just had to reset the clock, radio stations and auto wiper / auto headlight functions - all in handbook.)

It's worked perfectly ever since.

Where The XM Leads, Other Follow... - rg
The Series1 Citroen XM would give you all these electrical challenges way back in 1989....

The XM ahead of it's time?

I rest my case...

Where The XM Leads, Other Follow... - Armitage Shanks{P}
Yes but a Series1 XM would give you all those challenges without you disconnecting the battery - or have I missed the point here?
Where The XM Leads, Other Follow... - Dave N
I was working at a Renault main dealer the other day, and they were replacing the battery on a new Laguna. I asked them if they were using a code saver in the fag lighter. Nope, he said, we'll just code back in the electric windows manually. So who knows, some don't seem to mind, others do a bit, some do a lot.
Where The XM Leads, Other Follow... - jc
Someone asked earlier about Ford modules recalibrating themselves;I'll gire you some info.On ECU's without adaptive stategy-When you disconnect the module it loses everything it has learnt,for example, at idle,there will be slight differences between engines in the amount of friction in the engines and in the components fitted to the engines(top limit,bottom limit etc)so when you idle the engine,it takes a second or so to check the idle speed and CO and reset them to where they should be.With adaptive stategy it resets the criteria to where they were when the engine was last idling;this is why you need to run the engine in all conditions,not just idle,the engine must relearn all it's criteria.
Where The XM Leads, Other Follow... - Dave_TD
jc - It picks up air pressure, humidity, that sort of thing, yes? And driving style? Average throttle position, highest speed and revs reached? Does it grass you up to the service technician later?

Dave N - Everything needs to talk to each other? You're not kidding... I've looked over the mechanic's shoulder when he's been resetting my service indicator with his plug-in computer thingy, he's been running through a list of possible sources of fault codes, items on the display included headlamp levelling, wiper control, and radio! All well and good while it works, I suppose.
Where The XM Leads, Other Follow... - jc
Air pressure doesn't remember;measures air mass instantly-the latest types will remember driving style and,yes,will grass you to the technician.
Where The XM Leads, Other Follow... - BrianW
All this is very well if only one driver uses a vehicles.
In our case, and I suspect many households, we have two cars and three drivers and interchange frequently.
So the electronics would have to relearn driving styles two or three times a day and it would be all wrong when a change took place until the learning curve was complete. Although some usages may be short journey, say 4 or 5 miles, not suffucient for reprogramming to be completed.
Where The XM Leads, Other Follow... - rg
bring back the Morris Minor

(but even that had an electric fuelpump..)


Where The XM Leads, Other Follow... - Dwight Van Driver
Well said that man Govier

Where The XM Leads, Other Follow... - kithmo
bring back the Morris Minor
(but even that had an electric fuelpump..)

Yeah and you could reprogram it by hitting it with the heavy end of a screwdriver. ;-)
Where The XM Leads, Other Follow... - Clanger
please don't bring it back

don't even joke about it

Stranger in a strange land
Where The XM Leads, Other Follow... - timp
Haynes manual for Ford Focus suggests that you drive for at least 15 minutes at a variety of speeds, mostly concentrating on the 2000-4000rpm range, followed by 10 minutes at idle (while moving steering wheel occasionally and switching on high-powered equipment).

I wonder if there is an advantage of disconnecting and reconnecting the battery when you buy a used car, so it can 'learn' and 'optimise' iself to the new owner's driving style?

On the other hand, is the battery disconnected during electrical servicing, such as replacing the spark plugs? If this is the case, does the mechanic take the car for a drive while following the routine above? Would there be an adverse effect of not following the routine?
Where The XM Leads, Other Follow... - Ben79
I didn't disconnect the battery when servicing my car, but then again, changing the oil and air filter will have an effect on the car and require it to relearn the best parameters.

Where The XM Leads, Other Follow... - Cliff Pope
On any car, just in case, connect a spare battery with jump leads to earth and somewhere directly connected to battery positive, eg the starter terminal.
Remove the old battery, remembering that the loose positive terminal will be live, connect up new battery, remove jump leads.
Hey presto, job done, nothing is lost, nothing needs reprogramming.
With skill, the replacement battery itself can be used as the back-up, but that needs very careful juggling with the jumper leads.
Where The XM Leads, Other Follow... - DL
Cliff - a very sensible precaution - thus saving a lot of potential aggro....
Where The XM Leads, Other Follow... - Big John
I managed to flatten the battery on Erindoor's Punto 99 HLX a couple of months ago after leaving interior lights on for a few days. The battery was totally flat, no sign of life at all. GEM breakdown jump started me, I was worried about immobilizer codes etc...... It started instantly, the only side effect was that the trip computer and clock had reset and the radio took 10 seconds to read its code from the computer.

The breakdown guy said that most recent cars with fully integrated computers are usually OK, but he always had trouble with cars with earlier coded immobilisers and seperate radio/abs/central locking computers etc.. (mid 90's cars).

Where The XM Leads, Other Follow... - sean
I have to be very careful with what I post here.

You are absolutely correct with what you wrote.

And also with what you did not write.

Imagine a car that has had no development, other than styling, since the 70s.

Yes, the 70s.

Associate companies did intervene.

You are now seeing a bit more about me.

Watch what GM does. They saw something that I did.
Where The XM Leads, Other Follow... - DL
Sean - You been drinking? :-)
Where The XM Leads, Other Follow... - sean

How did you tell?

OK. What I meant was along the lines of no significant development, compared to their competitors, since the 70's.

I agree, not the same thing, at all.

I was wrong to say what I did. My views are mine and not of any associate.

I'm on the cusp of launching into technical details which would have been simple to sort by the owner of the breakthrough.

Fiat have a superb concept in the JTD multijet idea.

Lots of squirts into a flame. NO noise. Yes, really. And 300mpg.

Robert Bosch and Siemens are ready and waiting. Salivating. That part is true. Look at the previous injection systems. Jetronic and all that nonsense.


Ask Honest John

Value my car