Disco 2 BCU draining battery.

Been trying to diagnose a friend's td5 discovery. It's been killing the battery over 2-3 days. Initially I found a GPS tracking unit behind the rear quarter panel.. so binned all that which did help.. but not enough.

Using an amp meter between the neg and battery.. with bonnet switched bypassed.
Doors unlocked and open: 1.2a
Doors shut and locked (10 secs) 900ma
Doors shut and locked (10 mins) 390ma
Doors shut and locked (2+ hours) 390ma

I understand the BCU can remain active for up to an hour and a half so tried to rule the timer out.

Pulling fuse 20 under the dash reduces draw to next to nothing. Removed other fuses (radio, clock etc) to no avail. Interior lights (including glovebox) work properly.

No signs of water ingress on the interior fusebox, all BCU controlled components seem to work properly, except the window wipers. These are very intermittent as whether they'll work or not, although they always work on screen washer cycle. My personal assumption is a bad stalk.. but I could be wrong and this could be an interior fusebox issue.

Only other issue I have left now is the key fob receiver is failing and the key needs to be pressed against the rear window to work (new battery in fob) but I somehow doubt this would make much difference.

Any suggestions appreciated.

Jamiegreen said:

I understand the BCU can remain active for up to an hour and a half so tried to rule the timer out.

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Hi, that timing thing is for the SLABS ECU not for the BCU, the BCU is permanently under power as it's part of the alarm system. F20 is no factor for the BCU so if the drain goes out with F20 removed then IMO the BCU is ruled out, F20 is permannent feed for the interior lamps, passive coil, key in sensor and interlock unit(if fitted) ... at this point you should get to C0484 and unpin terminal 13 with the purple wire to see what happens cos that header used to have corrosion in it(i've seen cases when the purple wire which comes form F20 was at other pin so concentrate on the PURPLE wire) if the drain goes out with that wire removed and the header is clean inside check for corrosion at the interior courtesy lamps... are they working as they should on automatic mode too?

+1 to what Fery has said, but as you are having trouble with the fob receiver it is also worth unplugging the receiver and see if the current falls as it too is supplied from F20 via the BCU CO661-19.

@Jamiegreen ... Has your friend converted from air bags suspension to coil springs lately?

PopPops said:

+1 to what Fery has said, but as you are having trouble with the fob receiver it is also worth unplugging the receiver and see if the current falls as it too is supplied from F20 via the BCU CO661-19.

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good point, i missed to mention that one even though it's very strange which appears in the BCU description to be feed for RF receiver from F20 cos in the power distribution diagrams there's no circuit between F20 and BCU.... unfortunately the diagrams and WSM are contradictory quite often so better check than miss it.

sierrafery said:

... unfortunately the diagrams and WSM are contradictory quite often so better check than miss it.

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Agreed!

sierrafery said:

Hi, that timing thing is for the SLABS ECU not for the BCU, the BCU is permanently under power as it's part of the alarm system. F20 is no factor for the BCU so if the drain goes out with F20 removed then IMO the BCU is ruled out, F20 is permannent feed for the interior lamps, passive coil, key in sensor and interlock unit(if fitted) ... at this point you should get to C0484 and unpin terminal 13 with the purple wire to see what happens cos that header used to have corrosion in it(i've seen cases when the purple wire which comes form F20 was at other pin so concentrate on the PURPLE wire) if the drain goes out with that wire removed and the header is clean inside check for corrosion at the interior courtesy lamps... are they working as they should on automatic mode too?

View attachment 256931

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Ah my bad, probably should have looked what d20 does instead of relying on my memory.

Interior lights work properly on auto.
I've "removed" the purple wire from terminal 13. No bad corrosion in plug. And no effect on the current draw with it disconnected.

PopPops said:

+1 to what Fery has said, but as you are having trouble with the fob receiver it is also worth unplugging the receiver and see if the current falls as it too is supplied from F20 via the BCU CO661-19.

Click to expand...

I disconnected the reciever.. just the one small plug I could see if I'm correct, and no difference there.

JUKE179r said:

@Jamiegreen ... Has your friend converted from air bags suspension to coil springs lately?

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Still on air and working properly.

Jamiegreen said:

Interior lights work properly on auto.
I've "removed" the purple wire from terminal 13. No bad corrosion in plug. And no effect on the current draw with it disconnected.

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then it can be funny ... you'll have to go by the power distribution diagram and connector views and unpin the exits of F20 from the fusebox connectors (C0587-6, C0590-6, C0586-10) one by one and watch the drain to see on which circuit it's dropping....maybe you are lucky to not see any difference with all those wires removed then you know to change the fusebox otherwise it can become a nightmare

sierrafery said:

then it can be funny ... you'll have to go by the power distribution diagram and connector views and unpin the exits of F20 from the fusebox connectors (C0587-6, C0590-6, C0586-10) one by one and watch the drain to see on which circuit it's dropping....maybe you are lucky to not see any difference with all those wires removed then you know to change the fusebox otherwise it can become a nightmare

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I'd do that if I knew the proper way to remove the connectors from the plug.. one cable is one thing but multiple cables.. err, is there some sort of miniature locking tab on the pins?

Jamiegreen said:

I'd do that if I knew the proper way to remove the connectors from the plug.. one cable is one thing but multiple cables.. err, is there some sort of miniature locking tab on the pins?

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I dont understand what you mean, you have to unplug the connector and depin only the one wire which comes from F20, a very thin flat screwdriver can be used instead of de-pinning tool something like this but there are more videos find one for similar connectors

+1 again to what Fery said, but just a thought before you embark on a major event, has the audio head unit been changed recently, or any similar mods? F20 also feeds those units. If not, it will be unpinning...

sierrafery said:

I dont understand what you mean, you have to unplug the connector and depin only the one wire which comes from F20, a very thin flat screwdriver can be used instead of de-pinning tool something like this but there are more videos find one for similar connectors

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Sorry I misunderstood what you meant. Also do you happen to have the link handy which has the pictures of the connectors with the names? Can't remember the site.

Seems C0590 is the culprit at the moment. Will do a little more investigating as to which pin.

Jamiegreen said:

Sorry I misunderstood what you meant. Also do you happen to have the link handy which has the pictures of the connectors with the names? Can't remember the site.

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see connector views https://www.dropbox.com/sh/47hbz40an5he5j2/AAC8m5eHoojsOSxikJGWeXrHa/Electrical libary 03MY.pdf?dl=0

Thanks. I'll start removing pins tomorrow.

I have to get I fixed.. otherwise the owner is going to fit one of those god awful battery disconnects inside, I'm certain I won't let that happen

The easy way would be to plug in a known good fusebox cos it's the first suspect now, it's plug and play just to be from the same modell(facelift or not), battery disconnected first then after the swap and battery reconnection ignition on 2(not crank) for 5 minutes that's all

sierrafery said:

The easy way would be to plug in a known good fusebox cos it's the first suspect now, it's plug and play just to be from the same modell(facelift or not), battery disconnected first then after the swap and battery reconnection ignition on 2(not crank) for 5 minutes that's all

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I've got spare parts. But out of curiosity what makes you think the fusebox could be bad if disconnecting plug c590 from the fusebox kills the draw? I don't know which pin it is yet, but it's definitely in that plug.

Jamiegreen said:

....if disconnecting plug c590 from the fusebox kills the draw

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I didnt know that cos it wasnt clear from your previous posts, if disconnecting C0590 kills the drain then the fusebox is ruled out