Car computer issue

Submitted: Monday, Jan 23, 2006 at 14:41
ThreadID: 30007 Views:1661 Replies:6 FollowUps:6
This Thread has been Archived
Hi Guys,

I am looking for expert advice. The problem is this, I was working on my car (no not the Nissan) over the weekend and I had to disconnect the battery so that I could tighten the positive connection on the starter motor. All’s well and I reconnect the battery (hear a peep from the alarm), got in the car to find that everything needs resetting as expected. Take the car for a drive, had an errant that was 250K round trip, and find that the car is running much better than it has been for months (maybe years).

The question is, did I reset the car computer to factory defaults when I disconnected the battery? I presume that there would be any number of uncleared errors and the like and by resetting the computer I have cleared out this luggage as well. This seemed the most logical explanation I can come up with (a bit like rebooting the old puter when it is playing up).

This interests me because I can see that it could be useful when out in the scrub and the car is being temperamental. I’d like to hope that these black boxes are that simple and need a reboot occasionally to clear the clutter.

Can anyone shed any light on this?

Kind regards
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Reply By: revhead307 - Monday, Jan 23, 2006 at 14:51

Monday, Jan 23, 2006 at 14:51
your car must be running windows

better download the anti knock patch from the website.
and the security patch to stop hackers getting through your firewall.


AnswerID: 150308

Follow Up By: Member - Beatit (QLD) - Monday, Jan 23, 2006 at 14:53

Monday, Jan 23, 2006 at 14:53
I don't think so otherwise the darth vader of IT, Bill Gates, will have me doing just that and buying upgrades.

Kind regards
FollowupID: 403759

Follow Up By: gramps - Monday, Jan 23, 2006 at 15:03

Monday, Jan 23, 2006 at 15:03
Aaah but one of those Imperial Stormtroopers on your roof racks would be a pretty impressive anti-theft device :))))))
FollowupID: 403764

Follow Up By: Member - Beatit (QLD) - Monday, Jan 23, 2006 at 15:06

Monday, Jan 23, 2006 at 15:06
Too right gramps, but I suspect the rebelion they'd quell would be the one in the drivers seat.
FollowupID: 403765

Reply By: banjodog - Monday, Jan 23, 2006 at 15:22

Monday, Jan 23, 2006 at 15:22
You’ve pretty well answered your own question without realising it. Most late model cars running ECM / BCM (engine control modules / body control modules) require good clean 12v all the time.

You may have had a slight voltage drop from the connections on the battery terminal or wires from the starter motor – by reseating the connections on both you may have just brought everything back to normal.

Having electronics operating at less than 12v supply will give issues as the component won’t operate at it’s specified value which reflect in the vehicle's performance. As a starting point for any fault finding - what's the battery voltage and is there any voltage drop.

AnswerID: 150313

Follow Up By: Member - Beatit (QLD) - Monday, Jan 23, 2006 at 15:28

Monday, Jan 23, 2006 at 15:28
Hi Banjodog,

Thanks for that, I had not considered that the connection to the starter would affect the overall running of the car other than a huge voltage drop when trying to start the bugger through a poor connection.

Kind regards
FollowupID: 403768

Reply By: bazzle - Monday, Jan 23, 2006 at 15:55

Monday, Jan 23, 2006 at 15:55
Yes, disconnecting the battery for more than 30minutes will reset the computer.
Normanl to be done on MB etc.

AnswerID: 150320

Follow Up By: Member - Beatit (QLD) - Monday, Jan 23, 2006 at 15:59

Monday, Jan 23, 2006 at 15:59
Thanks Bazzle, I guess it makes sense that I should do this on a regular basis. Bit like cleaning up the desktop computer I would imagine.
FollowupID: 403775

Follow Up By: Notso - Monday, Jan 23, 2006 at 17:06

Monday, Jan 23, 2006 at 17:06
Actually I was told that the ECM is adaptive on most new cars and that it will adapt to a limited extent to your driving style as well.

So if you are a leadfoot it learns to accomodate your needs.

Anyhow I also noticed that with the Nissan patrol. Probaly because it got used to my lead foot and expected me to drive like that all the time. You don't notice little things when you are always putting the boot into it.

When I reset it it probably went back to a mid range state till it learnt my bad habits.
FollowupID: 403791

Reply By: Mike Harding - Monday, Jan 23, 2006 at 17:34

Monday, Jan 23, 2006 at 17:34
Can't say with certainty which will be reset and which will not but some variables will be stored in RAM memory which looses it's contents when power is removed and some will be stored in EEPROM memory which retains it's contents across power cycles.

It should do no harm at all to disconnect the battery from time-to-time to force the microprocessor to reinitialise variables and hardware. However some systems "learn" about their environment so it's possible it may have to go through that process again but that shouldn't be an issue – might even be useful.

Keep in mind that modern vehicles don't just have one microprocessor
they may have 10 or 20 of them scattered throughout the vehicle - some suspension systems, even, have a micro tracking them.

RAM and registers internal to the micro can become corrupt from a number of sources - electrical noise, cosmic particles (I kid you not :), software errors etc so why not give the little devils a full reset every six months or so? Ensure you disconnect the battery for at least one hour, better still overnight because some systems may use a capacitor to retain RAM for an hour or two.

Mike Harding
AnswerID: 150348

Reply By: techie - Tuesday, Jan 24, 2006 at 03:07

Tuesday, Jan 24, 2006 at 03:07
next door neighbour had a BMW which they replaced the battery and it wouldn't start - called the NRMA (no real mechanic available) he disconnected the battery for 10mins, reconnected, and it started no probs.
said every now and then they get the info scrambled and won't work.

AnswerID: 150501

Reply By: Member - Beatit (QLD) - Tuesday, Jan 24, 2006 at 10:21

Tuesday, Jan 24, 2006 at 10:21
Thanks guys, mechanical components are one thing but the puter and its sensors are entirely something else for me. This thread has shown me that disconnecting the battery is not a bad thing, in fact, most likely something I will do more often.

Kind regards
AnswerID: 150523

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