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7th February 2021, 07:54 | #1 |
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Parasitic battery drain - where to start?
Hi all,
I noticed my battery seemed to be dying, so switched it out for a new, high quality one, only to find that seemingly can't hold any current either. I read the issue could be due to a parasitic drain, and sure enough, after connecting a multimeter between the negative pole and cable, I have an initial 400 mA drain (which I read is normal), which soon settles down to around 110 mA. From what I've read, that's a lot higher than it should be. I know the received wisdom is to start pulling fuses until you see the figure drop, but I was just wondering if there was a list, or anything similar, of the fuses that are most likely to cause issues, to help me target my search? I've tried all the fuses under the bonnet, have disconnected the alternator from the circuit entirely, and tried a handful in the passenger footwell (alternator, one I think was the radio etc (as I have an aftermarket sat nav), and a few more) That's assuming the 110~ mA drain isn't some sort of circuit activating when you make the connection like the initial 400 mA drain, and it just takes forever to drop down! |
7th February 2021, 13:42 | #2 |
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Parasitic Battery Drain
I have a similar problem, without using the car daily it only takes about 4-5 days before the car is a non-starter and she requires charging or a jump start.
I had the RAC sell me a "High Quality, High Amperage" battery, for which read " High Cost!" whilst stuck in the middle of Dartmoor on holiday last year. I pointed out to the RAC tech that the car has a problem in that the drivers info panel LED's remain lit when the ignition is turned off (that's the outside temp/trip mileage and odometer bit). He measured the battery drain and declared that at .5amps it would be no problem and the battery was guaranteed to start the car for at least five years, yeah right!! Does anybody have any suggestions as to how to test this, how to rectify this or should I just start practising for when I have to go all electric and just plug the car in every night? |
7th February 2021, 15:24 | #3 |
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I checked out my cdt recently the drain was 30 ma I think that is ok. But sorry I dont have list of likely sources of leak.
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25th February 2021, 07:13 | #4 |
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OK! So, after following the forum's general voltage drain-related advice, I started pulling fuses out over the weekend, and I think I've found my draw. The only problem is, I don't really know where to start in tracing it.
Originally, the drain I was seeing as about 100mA, after it had been left to settle. All the fuses that seemed to be causing issues were behind the passenger glove box. Pulling fuse F5 (BCU, wipers) dropped the voltage by 50mA. Pulling fuse F14 (central locking) dropped it by 10mA. Pulling F24 (front windows) dropped it by 10mA Pulling F21 (power seats) dropped it by 20mA And pulling fuse F20 (fuel pump) dropped it by another 10mA. Now, I know that some residual drain is normal, so I'm assuming some of these fuses aren't issues. I'm also guessing fuse F5 is my most likely culprit, which the manual simply describes as "body control unit". All I'm wondering is, how do I go about tracing the fault with the body control unit? And which of the other fuses are normal drains, and which need to be investigated further? Last edited by ianM; 25th February 2021 at 10:02.. |
25th February 2021, 08:24 | #5 |
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Body control units are very reliable, in fact in all the years I've been seeing these cars, I've only ever had to change two
The first was because somebody had taken the BCU out for some reason and knocked a component off the board, the second was a tourer prototype unit that never worked correctly from the factory. Parasitic battery drain problems can be a pain to find, my best guess is that there's obviously something interfering with the K-bus that's keeping the car awake. On your post you haven't listed the cars equipment which may help narrow down where possible problems may be. Fuel burning heaters on diesels are favourite, as are sat nav drives on cars fitted with highline. I've had two cars recently with similar problems, one was the Sat nav the other was a fuel burning heater Russ
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25th February 2021, 10:04 | #6 |
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Hi Russ,
Thanks for the suggestion! It's a V6 so not a fuel burning heater issue, and although it was originally a hi-line model, I've got an aftermarket unit fitted now so the sat nav unit in the boot shouldn't be an issue. I was under the impression those were on different fuses too - I've just updated the post using info from this post about what each fuse is apparently related to. I was just wondering if anyone knew what a normal draw was for each of these (should the memory seats be drawing 20mA all the time?). With regards to the BCU, I imagine something is probably keeping it "awake" and stopping it turning off as you say - it's just knowing where to start really. Another thread mentioned the wiper motor contacts being gunked up and basically shorting as being their issue, with very similar symptoms to me, so that's my first point of call. |
1st March 2021, 11:52 | #7 | |
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Quote:
I'm glad that you posted this. My quiescent current (after the first 20 minutes as specified by MGR) is o.k. but every minute or so it increases to 100 mA then drops again. Unplugging the wiper motor connector reduces this. There is a feed from the wiper motor parking switch to the BCU which I was about to investigate when my OSF spring snapped! Simon
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1st March 2021, 12:47 | #8 | |
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Quote:
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1st March 2021, 16:11 | #9 | |
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Quote:
Hi Simon, Sounds at least fairly similar to mine! Rather than only going up every now and then, though, mine was at a pretty constant 100mA draw - after a bit of investigation at the weekend, unplugging the wiper motor does fix the problem, leaving me with a residual 50mA draw - something I guess is at least closer to being normal, if not quite there yet. I'm planning on spraying some contact cleaner on it when I get chance, to see if that solves the problem - hoping it's not a problem with the wiper motor itself! |
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15th March 2021, 09:52 | #10 | |
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Parasitic Battery Drain
Quote:
Took it to local Auto Diagnostics fellow today, he plugged it into his computermajig and after clearing a load of old fault codes and checking her over he believes the fault lies within the instrument cluster unit and recommends trying a replacement (either new ££££££, or second hand £) to see if this closes the problem out. However having read the above reference the BCU etc should I be looking at that? Does the instrument cluster get its info from the BCU so that if I do change the cluster will it still show correct mileage or is that stored in the cluster and will show whatever the donor vehicle/new cluster has recorded? Hmmm |
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