Dead battery and jerky engine

U

ulfurk

Member
My battery was dead following being stored for about 6 months.
We gave it a jump and it started up just fine.
We drove around for a bit and hoped it would have gotten a bit of charge.
No luck and the next time I went to start the car it was completely dead.
Tried jumping it again with no success, the started just clicked continuously but obviously did not muster enough power to start the car.
Took the battery out and charged it up using a charger and put it back in.
Now the car is behaving like nothing I've seen.
The engine jerks rhythmically between 500 and 1000 rpm and pressing the accelerator has no effect at all.

I'm scared I've messed up the ECU or alternatively it could be a faulty flow sensor or something of the sort although I have a hard time seeing how the preceding events could have caused that. Secretly I'm hoping it's just a state it's gotten into and can be "reset" or will somehow magically resolve itself.

Any thoughts or ideas?
 
Firstly the battery will be shagged - bin it and get a new one. The charging circuit can't recover it after its been flattened like that and for so long.

Secondly it will probably have gone into transport mode....easy way to tell is that heater only works on lowest speed. Dealer needs to reprogramme it, costs around £35.

Thirdly, I had the same symptoms engine-wise when it happened to me, but with a new battery the symptoms vanished for good after a couple of miles.
 
Thanks for the advice. It sounds highly likely that this is what's happening.
I also have to admit that my description wasn't completely accurate last night.
I didn't actually put my old battery in but took the shortcut of replacing it with another, perfectly good but slightly smaller, battery I had lying around.
After thinking about it for a bit I have a suspicion the battery I put in may have a lower current rating than the original and this may be causing the strange behaviour, if only partially.
The original battery was responding last night and charging normally so I have hopes that it is still good and hopefully once I pop it back in the strange symptoms will disappear.
If they persist I have a friend coming over who has the software and cables required to connect to the ECU which should then provide further information on whether it is indeed in Transit Mode or if it is something more serious.

In any case, thanks again for the help and I will post an update as soon as I know more.
 
ulfurk said:
Thanks for the advice. It sounds highly likely that this is what's happening.
I also have to admit that my description wasn't completely accurate last night.
I didn't actually put my old battery in but took the shortcut of replacing it with another, perfectly good but slightly smaller, battery I had lying around.
After thinking about it for a bit I have a suspicion the battery I put in may have a lower current rating than the original and this may be causing the strange behaviour, if only partially.
The original battery was responding last night and charging normally so I have hopes that it is still good and hopefully once I pop it back in the strange symptoms will disappear.
If they persist I have a friend coming over who has the software and cables required to connect to the ECU which should then provide further information on whether it is indeed in Transit Mode or if it is something more serious.

In any case, thanks again for the help and I will post an update as soon as I know more.
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I think just one or two of the third party software packages will let you get it out of Transport Mode but otherwise its the dealer.

If your aircon and circulation fan is working fine on all speeds though you have probably been lucky. If not, fan only runs on slow speed.

Mine coughed exactly like that even with a new battery but it vanished after 3-4 miles or so and never came back.
 
Hey guys and thanks again for your replies.
So I checked the battery and it was at full capacity and had charged up just fine. Yay for that!
However, when I had it back in the strange behaviour persisted.
Luckily I had my mates ODB2 device on hand and plugged it in.
It gave me a single error code to do with a failure to read the accelerator properly.
In a leap of faith I decided to hit "Clear Error Codes" betting that the error code just resurfacing should it be an actual problem.
Started the car and... presto, runs like a dream, everything back to normal.

So there you have it. If the power goes completely out on your car for a longer or shorter period of time chances are that it'll upset the ecu and the array of onboard sensors but it may not be serious at all.
In case of failure to provide adequate power to this intricate system it may simply start making bogus assumptions on the state of affairs and toss up error codes that aren't necessarily accurate once the system is getting the power it needs.

All the best and much thanks for your replies :)
ulfurk
 
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