Battery drain by Devilish

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Have had this problem since last year, battery going flat, after 5 days will just about start, after 7 days, battery is flat. Was in the garage not used November-April, middle of November, came to move it, flat battery, charged it, a week later flat battery. So I just disconnected the battery, re connected it end of May and hey presto.
Meter shows a drain of 3.8amps. With the BCU (Body Control Unit) asleep I pulled every fuse and relay in both fuse compartments one at a time, drain remained at 3.8a.

No FBH (Fuel burning heater.).
NO satnav.
No CD changer.
Not battery, charge rate, multimeter, or battery terminal/alternator connection resistance.
Disconnected all electrical mods.
Disconnected the towing electrics power supply and lighting relay.
Plenum chamber dry as a pharaohs sandal.(always has been)
Lifted the under bonnet fuse compartment and nosed around the wiring looms.

I know it will be difficult (well it would for me) but at least try to resist suggesting the hokey cokey, tilting my head to the side, squinting, standing on one leg, touching my nose with my index finger etc etc etc, but if you must.........

Drain remains at 3.8a.

In the morning I will pull the glow plug relay and the ECU (Engine Control Unit).

Any suggestions while I still have some hair left.
If at first you don't succeed, hide the evidence.

Posted 06 Jul 2016, 17:59 #1 

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Hi Steve.
When you disconnect the Glow plug relay,module open it up and check to see if all is ok inside no corrosion etc,
There are five locking lugs three one side.

Two the other

Another chance to use those tooth pics :-o

Once you have it open slide out the pcb board

Check the board both sides for corrosion


I have heard these can get stuck in the on position how true I don't know, anyways we as in me and Stef are about tomorrow from 10.30 onwards if you wanted to have a drive over, T4 (Testbook version 4.Computer Diagnostic System) will be out as stef is adding some clocks to his MGZT.

We could hook it up and see if it tells us anything ?

Posted 07 Jul 2016, 01:29 #2 

My wifes 45 suffers from this - still have not checked out where the draw is - Maplin sells a unit whereby you pull a fuse, fit one linked to a meter and it shows the draw. However, hers is a petrol model so no glowplugs. Will be interested with what you come up with.Did wonder if it could be the battery backup sounder.

That apart Mrs Lincoln, did you enjoy the play


Posted 07 Jul 2016, 11:27 #3 

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Some good ideas there Steve. If the glow plug relay was sticking on I'd expect the current to be way higher than 3.8A though.

Steve, have you tried taking the big fuses (red and green with a clear plastic lid) and even the screw in fuses out of the under bonnet box? Some things run straight from them without going through a smaller fuse.

Posted 07 Jul 2016, 19:49 #4 

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Steve will no doubt be along later but yes he has taken out all fuses and I mean all of them , also disconnected the alternator, glow plug relay and still the same so he is now stumped, mine goes flat after a few days too but is normally used everyday so I don't notice it as the car only gets left unused for a few days about once a year. His battery is fine as if left disconnected it loses no charge
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Planning is an unnatural process, much better to just get on with things, that way failure comes as a complete surprise instead of being preceeded by a period of worry and doubt

Posted 07 Jul 2016, 20:59 #5 

Last edited by Trebor on 09 Jul 2016, 13:54, edited 1 time in total.

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Well I lifted the ECU and disconnected the glowplug relay, unplugged the ECU, and not even a drop of a milliamp.
I had previously removed FL1 through 12, as well as all the other fuses and relays.

I have checked the battery drain on 2 other diesel 75's one had a battery drain of 2.2amps, the other had exactly the same drain as mine, both vehicles are used every day. At the last nano, someone approached me saying they had a almost 4 amp battery drain and if not used his battery goes flat. Not much I could do as I had the same problem. I am going to test the drain on a V8 today whose battery goes flat if left 7 days or more. my guess it will be the same.
I have been told by another owner that his battery goes flat if left longer than a week.

So do they all drain the battery flat if not used for longer than 1 week?

Steve, At 10:00 I have a broken powerfold mirror to look at, and possibly a charging socket to install, I will give you a call when I am done. Have not used it since Sat and I reckon the battery will be flat.

Batterey is a 12 month old 77ah S5
If at first you don't succeed, hide the evidence.

Posted 08 Jul 2016, 07:12 #6 

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(Site Admin)
Dunno about diesels Steve. My V6 hasn't drained flat in 12 years. On second battery, first lasted 7 years. Car is often left for a week or more between trips.

Posted 08 Jul 2016, 15:59 #7 

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My V6 has some kind of drain and I have to disconnect the battery if I leave it for more than 3 or 4 days, the diesel is OK for at least two weeks and will still start after 3.

Posted 08 Jul 2016, 17:10 #8 

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I've looked at the circuit diagrams. Apart from some odd things inside the under bonnet box that there's no explanation for, it shows all electrical systems are fused from one of the small medium or large fuses. You could try removing relays as well, and at a push lift out the under bonnet fusebox and start pulling the connectors from the back. If you have a clamp meter you could try measuring each of the wires coming out of the fuseboxes, though this will clearly take a while. 3.8a is 45 watts, so its something big! In theory you battery should be flat in half a day at that rate.

Posted 08 Jul 2016, 17:41 #9 


That apart Mrs Lincoln, did you enjoy the play


Posted 08 Jul 2016, 18:54 #10 

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We are now in October. Did anybody find out where these big voltage losses are ??

There should be some heat generated too at those amperages.

Posted 05 Oct 2016, 20:23 #11 

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I tested about a dozen diesel 75/ZT's all had the same drain reading as mine. I returned the battery in September, the conversation went like
"This battery goes flat in 3-4 days from fully charged"
"The tester says battery is flat"
'REALLY' quick look round for Jeremy Beadle
"It was fully charged 3 days ago"
"Look the meter says it is flat and just needs charging"
"I am fed up of charging it"
"what do you use to charge it"
'A Christmas tree light adapter'
"Well the meter says the battery is ok and needs charging"
"and I am supposed to do what, charge it every time I want to use the car"
"I will go and ask the boss, back in a bit"
'come back and tell me it is flat once more' :roll: .......
"Ok we will exchange it for another"

Left it until trebor took it to Prescott for me on 02/10, ok.
I used it on about 10/10, ok.

Engine turns over much faster than the other battery when fully charged.

I Will use it for the nano the weekend.

I want to see a diesel with a 50+mA drain

Duncan, the battery may have gone flat in a day, but I only use it once or twice a week.

I intend to pop the meter on with the new battery, to see if the drain was related to the "Good battery that is just flat"
If at first you don't succeed, hide the evidence.

Posted 14 Oct 2016, 07:32 #12 

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Devilish----------------Keep us posted.

Posted 21 Oct 2016, 12:52 #13 

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Colvert wrote:Devilish----------------Keep us posted.

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Posted 21 Oct 2016, 12:57 #14