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Discussion Starter #1
Came back to my car this evening after work to find it dead. Quick check on underbonnet terminals showed battery to be at 5.6v. RAC guy was able to demonstrate a significant draw of between 4 to 8 amp even when car is switched off and locked. This was occasionally coupled with the familar clicking relay sound from the boot. Not really sure how to trace why the ECU would be staying awake like this. He noted the car appeared to attempt to shut down as draw falls from 8 to 4, then a few seconds later it wakes up and resumes the 8 amp draw.

12v battery is Bosch S5 and under 1 year old - RAC diagnostics showed it to be in good health, and to be honest the issue is almost certainly the parasitic draw rather than the battery itself.

Don't recall reading about any such issue before - does anyone else?
 

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Not heard of this before, could it be a faulty relay/contactor with the terminals welded together?
 

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Discussion Starter #3 (Edited)
Not heard of this before, could it be a faulty relay/contactor with the terminals welded together?
Once 12v recharged the car powers up and down fine - so doesn't seem to be the HV contactors. I guess it could be some other relay that powers some 12v equipment. I could do with a meter to measure current draw like RAC used. Only way I can think of is to use a cheap multi-meter between battery negative terminal and the cable but I don't really have the right clips etc to do this properly. Not sure if the cheap clamp testers on Amazon would be able to measure a 5 amp DC load? That would be a lot easier than disconnecting battery cables.
 

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Ampera aka IGOR
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Could you have somewhere at work where the car could still be picking up the signal from the key for the keyless entry and so keeping the car awake waiting on a door button being pressed?
 

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Discussion Starter #5
Could you have somewhere at work where the car could still be picking up the signal from the key for the keyless entry and so keeping the car awake waiting on a door button being pressed?
Thanks, I think it might be exactly this. Though no way my key was in range (a good 70 meters away - and the same its been for a couple of years with no issue). But perhaps some local interference that kept the car awake looking for the key. Going to test current draw at home and ensure it drops to typical 'shut down' levels. It was at 11v this morning so unsure if that was because its 0 degrees or there is still some drain.
 

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Discussion Starter #7
11 volts seems as though it is getting too low, could there be something internally up with the battery?
RAC test equipment said the battery was in good health. But he tested the draw with car locked and all off - and was fluctuating between 4 and 8 amp - way too high (should apparently be max 0.5 amp when car off). So something was preventing car from shutting down.
 

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Would be worth disconnecting the 12v completely to a) check it out standalone, and b) reset the car if there's anything gone glitchy in the software.
Does the car draw this high current when sitting unlocked & switched off on the driveway? If so, I'd be tempted to put a current meter in, and start removing fuses one-by-one to try & isolate exactly what circuit is drawing so much power. Sounds an awful lot just for one door catch...
 

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Discussion Starter #9
Would be worth disconnecting the 12v completely to a) check it out standalone, and b) reset the car if there's anything gone glitchy in the software.
Does the car draw this high current when sitting unlocked & switched off on the driveway? If so, I'd be tempted to put a current meter in, and start removing fuses one-by-one to try & isolate exactly what circuit is drawing so much power. Sounds an awful lot just for one door catch...
So I do need to investigate further. Do you think a clamp meter (excuse me if I've used the incorrect term) be able to measure this sort of current draw without disconnecting the negative terminal from the battery? If so I can borrow a pro-grade one from an electrician friend.
The only other way I can think of is to remove negative clamp from battery and using crocodile clips link through my cheapo multimeter - remembering not to power on the car or activate anything remotely power hungry...
 

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Borrow the meter.... The multimeter is probably only capable of 10A and that for very short periods. 10A could easily turn up in a 12v System. The proper clamp meter will show whats happening safely.
 

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Discussion Starter #11 (Edited)
So last night I attempted to disable the keyless entry however its only possible to disable it on passenger doors. Doing that however does seem to have solved the issue (battery over 12v this morning). So current theory is water ingress into a door handle button is activating the ECU to search for the key, ramping up power until giving up and going back to sleep. The process seems to repeat until battery dies.

@Gingerdave may or may not have same underlying issue. Perhaps on Sunday I will strip the (passenger) door handles down to check for issues. @HandyAndy did warn me when fitting the replacement door handle switches I may end up re-doing this due to my not insulating the connections very well!

Edit: just discovered that my disabling of 'other doors' keyless entry does not actually disable the buttons. Pressing one still wakes up the ECU. I will still have to disassemble the handles as this still seems most likely explanation.
 

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Would be worth disconnecting the 12v completely to a) check it out standalone, and b) reset the car if there's anything gone glitchy in the software.
Does the car draw this high current when sitting unlocked & switched off on the driveway? If so, I'd be tempted to put a current meter in, and start removing fuses one-by-one to try & isolate exactly what circuit is drawing so much power. Sounds an awful lot just for one door catch...
 

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This could be a long shot but I had the same sort of problem with my old motorbike.
The battery went flat for no reason.
I eventually found the key fob was fault and transmitting all the time,keeping something “on “ on the bike.
New key fob and it’s fine.
Try pulling the battery out of the key fob.
 

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Discussion Starter #14
This could be a long shot but I had the same sort of problem with my old motorbike.
The battery went flat for no reason.
I eventually found the key fob was fault and transmitting all the time,keeping something “on “ on the bike.
New key fob and it’s fine.
Try pulling the battery out of the key fob.
Guess I could test for that by leaving keys in a tin well away from the car. It's a possibility I guess. My prime suspicion at the moment however is water ingress into the door handles triggering the keyless entry buttons. This is mostly because of the way I carried out a repair to the buttons. But it's not a fact until I strip one down and see if there actually is any water in there. Planning to do tomorrow depending on the weather...
 
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