Go Back   The 75 and ZT Owners Club Forums > The 75 and ZT Owners Club Forums > Technical Help Forum
Register FAQ Image Gallery Members List Calendar Mark Forums Read
Notices

Reply
 
Thread Tools Display Modes
Old 7th February 2021, 08:54   #1
ianM
Regular poster
 
Rover 75 2.5L V6 Saloon; Rover 214i

Join Date: Sep 2010
Location: West Midlands
Posts: 86
Thanks: 18
Thanked 1 Time in 1 Post
Question 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!
ianM is offline   Reply With Quote
Old 7th February 2021, 14:42   #2
Muttley
Regular poster
 
MG ZT 190+

Join Date: Jan 2017
Location: DERBY
Posts: 95
Thanks: 56
Thanked 19 Times in 14 Posts
Default 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?
Muttley is offline   Reply With Quote
Old 7th February 2021, 16:24   #3
Cantray
Avid contributor
 
Rover 75 1.8 Club SE, Rover 75 cdt Club, Rover 75 1.8 Connoisseur SE

Join Date: Jul 2015
Location: Inverness
Posts: 163
Thanks: 48
Thanked 44 Times in 27 Posts
Default

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.
Cantray is offline   Reply With Quote
Old 25th February 2021, 08:13   #4
ianM
Regular poster
 
Rover 75 2.5L V6 Saloon; Rover 214i

Join Date: Sep 2010
Location: West Midlands
Posts: 86
Thanks: 18
Thanked 1 Time in 1 Post
Default

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 11:02..
ianM is offline   Reply With Quote
Old 25th February 2021, 09:24   #5
BigRuss
Premium Trader
 
BigRuss's Avatar
 
75 CDT Tourer,2.5 Launch Saloon, Omipro MG/Rover (T4)

Join Date: Jul 2007
Location: Liversedge, West Yorkshire
Posts: 5,405
Thanks: 1,105
Thanked 1,340 Times in 661 Posts
Default

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
__________________


Replacement Key Service
http://https://the75andztclub.co.uk/...d.php?t=244732
Full T4 Testbook diagnostics available.
Diesel ECU repair and replacement.
Options enabled or disabled as required.
Diesel X-Power 135 and 160bhp, Rover 1.8T 150 to 160
MG 160 V6 to 177 upgrades available
P.M. for details.
BigRuss is offline   Reply With Quote
Old 25th February 2021, 11:04   #6
ianM
Regular poster
 
Rover 75 2.5L V6 Saloon; Rover 214i

Join Date: Sep 2010
Location: West Midlands
Posts: 86
Thanks: 18
Thanked 1 Time in 1 Post
Default

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.
ianM is offline   Reply With Quote
Old 1st March 2021, 12:52   #7
SD1too
Doesn't do things by halves
 
SD1too's Avatar
 
Rover 75 2.5 Connoisseur Auto (1999) Dealer launch model.

Join Date: Mar 2007
Location: Former Middlesex
Posts: 20,272
Thanks: 1,587
Thanked 3,749 Times in 3,181 Posts
Default

Quote:
Originally Posted by ianM View Post
With regards to the BCU, I imagine something is probably keeping it "awake" ...
Hello Ian,

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
__________________
"Whatever is rightly done, however humble, is noble."
Sir Henry Royce.
SD1too is offline   Reply With Quote
Old 1st March 2021, 13:47   #8
edwardmk
Gets stuck in
 
edwardmk's Avatar
 
MG ZT 260, Rover 75 Connie SE auto

Join Date: Feb 2013
Location: Redruth
Posts: 982
Thanks: 1,324
Thanked 399 Times in 271 Posts
Default

Quote:
Originally Posted by SD1too View Post
Hello Ian,

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
Hi Simon. Is the BCU the same as the BCM, namely the computer module that controls things like door locks etc? I've noticed current twitches and pulses more than 30 minutes after locking up the V8.
edwardmk is offline   Reply With Quote
Old 1st March 2021, 17:11   #9
ianM
Regular poster
 
Rover 75 2.5L V6 Saloon; Rover 214i

Join Date: Sep 2010
Location: West Midlands
Posts: 86
Thanks: 18
Thanked 1 Time in 1 Post
Default

Quote:
Originally Posted by SD1too View Post
Hello Ian,

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

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!
ianM is offline   Reply With Quote
Old 15th March 2021, 10:52   #10
Muttley
Regular poster
 
MG ZT 190+

Join Date: Jan 2017
Location: DERBY
Posts: 95
Thanks: 56
Thanked 19 Times in 14 Posts
Default Parasitic Battery Drain

Quote:
Originally Posted by Muttley View Post
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?
Further to the above I have checked all of the instrument/dashboard fuses, all are okay.
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
Muttley is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 14:08.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © 2006-2023, The Rover 75 & MG ZT Owners Club Ltd