Sorry for the size of my post
The Problem:-
My car will unlock with either fob the car cranks and starts easily and everything works.
However if I switch off then the fob will not lock or unlock the doors, the car will not crank / start - not even a click. However the stop lights come on and remain on.
After allowing a suitable "go to sleep " period if I disconnect the battery and connect the +ve and -ve leads together for a short time everything works again -i.e.the car will start and the key fob operates the door locking as normal.
Switching off causes the non start condition to occur again and can be "fixed" again as above.

The first time this problem occurred I had to call on the RAC he couldn’t find the fault and couldn’t understand why the stop lights had come on but reset everything and it started.

I was already aware of a parasitic drain issue and had removed fuses 49 and 27 however the RAC found the battery fully charged so I did not associate this with the problem.

I fitted a recon starter and new AGM battery and this seemed to resolve the starting problem although I still needed to investigate and sort the parasitic drain issue .

Some days ago whilst out I found that the washers didn’t work, when home I checked out fuse 47 which was OK. I then replaced fuse 27 and the washers worked but on switching off I got the problem described above and nothing I have tried fixes it including adding an additional earth strap, replacing fuse 49 and 27, cleaning earth points.
I would like to look at the BCM but can’t find it

I would invest in a new stop-light switch as they often fail and are cheap enough to try even though probably not the cause.

Thanks for the response and suggestion, it's a complicated beast so I am hoping someone on here has come across this before

How about the the ignition switch?
A couple of years ago my 3.6 had a series of intermittent seemingly unconnected electrical issues. These continued until the ignition switch failed completely, when the switch was replaced all of the other gremlins disappeared at the same time

It could be the switch but as that looks to be a difficult job I am trying other possibilities first. At the moment I would like to find the BCM.
Today I went for a drive but when I got back exactly the same problem.
I removed the battery completely and unplugged and cleaned the relays and fuse holder behind the battery - they all looked very clean and predictably did not solve my issue.
I have also tried other suggestions including trying in neutral - no good and switching on the windscreen wipers again no good.
I am searching the web for the location of the BCM and considering removing the fuse box to check for water ingress.

Very disappointing especially as my Disco 2 never missed a beat .
Thanks again if I don't resolve it I have a potential garage lined up but they are closed at the moment.

Punching in the dark a little here, but, can you disarm the alarm/immobiliser, central locking to see if that makes a difference? Try & leave your car unlocked overnight (scary I know) then start-drive-restart the next day without unlocking the car (process of elimination)? What I'm trying to do is elimate or highlight who or what is playing silly b's? Another wild thought is a sticky relay (if that actually exists?)........as I say, punching in the dark. 2012 Orkney Grey Westminster 4.4TDV8 with Ivory interior.........nice!
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The BCU should be under the front passenger seat judging by the diagram in the parts catalogue, although I wonder what you might do in the way of checking it other than re-plugging its connectors.

Hi Fox889, no sure how to do that and as you say scary.

When I have stopped the car and switched off I can open close doors with the dashboard button but not with either of the fobs so I could leave it open but not sure whether this disables the alarm. At the moment I leave it 10 mins to go to sleep then disconnect the -ve terminal then after another 10 mins do the ecu reset and leave it with the -ve disconnected until I want to start it. I plan to check the LCM and BCM next but so far have not found them.

Thanks again for your post, I am working thru the past history on this site to see if anyone else has had something similar.

Hi GraemeS,

Thanks for the info,
I was planning to check for corrosion and clean the contacts on both the BCM and LCM. I have watched the video showing it being removed but there's nothing like that under my seat.

I have been told that in the 2009 models it was relocated possibly behind the fuse box.

One of the old posts where the stop lights were on with the ignition off found a fault in the CAN wire where it had chaffed on a sharp bit of body.

It's a bit of a mystery at the moment why everything works after an ecu reset but packs up after switching off.

I presume you do not have any diagnostic equipment? Without checking for codes your playing guessing games im afraid...

For what its worth, i think your correct looking into the BCU BUT! it may simply want reflashing? But again you need diagnostics sir...

All that's happening when you do your reset is that power is cut from all the modules draining their storage capacitors within the 1st half a second or so of the first battery lead being disconnected thereby forcing a cold start of the modules when power is reconnected. Whatever is going wrong is leaving a module in a messed-up state which is cleared on a cold start.

The brake switch is a common cause of strange faults because it has 2 sets of contacts, 1 set closed when the pedal is at rest and the other open, then vice versa when the pedal is pressed. If 1 set isn't operating correctly then mixed messages are sent to the BCM and various other modules, hence my earlier suggestion to replace the switch as it is a low cost item that is easily changed. Just be sure to follow the fitting instructions as the switch is preset for fitting and whilst it can be reset, if it isn't set properly then it won't work correctly once fitted.

Hi Graemes and Craig, firsly thank you for responding to my problem,
you are right I don't have a diagnostic tool I have downloaded 3 earlier posts / replies which are not exact matches but may provide some clues, the comments from Weejock are interesting he states that the brake lights do not go thru the BCU he is pointing to the ABS I have printed the post to read it more thoroughly, a second contributor found a short in the MS Can bus wire near the parking aid ecu - again printed to read and check out sorry credit to Buck66 and a damp LCM problem from andyfid and stop lamp switch.
Plenty to keep me busy as I stay at home
With respect to diagnostics, there are small units on ebay of varying price but it is not clear to me anyway whether these require further software to enable information to be read. I watched an excellent video from RSW solutions which was based on suspension problems and recalibration of ride height, that required software from US and a reader approx. £25 ELM327

sorry GraemeS thanks for the tip about following fitting instructions with the sl switch. The car is full of sneaky traps, I have been told not to trial a used BCM as this will imprint my car with the mileage of the car it was taken from!
Have a nice day

I do think you’d be better off with an IID tool or something of that ilk! Trying to diagnose a fatty without diagnostics is much harder, if not impossible! And if it simply wants the BCU or LCM reflashing, you cant do that without a decent tool!

Just my 2peneth worth sir... 👍

You may need to use a diagnostic tool that provides live values to see what is not correct when trying to restart if no faults are stored, but hopefully 1 or more fault codes will point to a particular fault.