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Discussion Starter #1
Hi Everyone,

I apologise in advance for the long post but this issue is rather complex.

I'm hoping someone might be able to help me with an issue that I am having with my 2005 Range Rover that appears to be causing the battery to drain. I’ve scoured the internet for similar issues but I just can’t find anything that matches the symptoms.

I'm noticing that the PRND lights below the gear shifter are turning on randomly well after the time it should take for the BCU to shut down. I’ll go out and look through the front windows of the car hours after leaving it and most of the time the gear selector lights are on – even though the car has not been touched for hours. I’ve stood outside and watched the lights for almost an hour and they randomly turn off and then turn back on shortly afterwards. The car is kept in a secure garage so I don’t lock it but the same issue happens if the car is locked.

I assume this is an indication that something is waking-up the BCU? I had the BCU replaced with a brand-new unit a few months ago because I was having issues with the rear doors not unlocking and the power steering not working. Since then, both of those issues have been rectified but this battery drain issue has started. The Rangie isn’t my daily driver and I only drive it every few days but I used to be able to leave the car for weeks without the battery draining but now it’s dead after 3-4 days. The battery is less than 12 months old and is a good quality Varta Silver Dynamic H3 100Ah 830CCA which I regularly charge using a CTEK MXS 5.0 and have had checked by a battery specialist so I know the issue isn’t battery related. The alternator has also been checked and is good.

I also notice when I am working on the car with doors open that the interior lights will shut-off after about 20 or so minutes which I believe is a feature of the car to prevent interior lights draining the battery if a door is left open; however, after another 30 or so minutes without opening or closing any doors or pressing any buttons – all of the interior lights will turn back on and it sounds as if the cars systems are starting up (computer fan noise coming from near HVAC controls). I’m not sure if this is supposed to happen but could be the same issue perhaps?

According to the L322 Range Rover workshop manual, these are the things that could cause the BCU to wake up from sleep mode:
• The K bus – so many things on this – not sure where to start
• Any door status switch (driver, front passenger, LH and RH rear doors)
• Bonnet status switch – replaced
• Central door locking switch – haven’t checked this but it works perfectly
• Driver's door lock cylinder lock switch – works perfectly
• Driver's door lock cylinder unlock switch – works perfectly
• Interior lamp switch – no interior lights turn on when the PRND lights come on
• Lower tail gate opening switch – checked
• Tilt alarm sensor – don’t think it’s this because the issue occurs when the alarm is off, too.
• Ultrasonic sensor – same as above
• Upper tail gate opening switch – replaced with a brand-new part
• Upper tail gate status switch – replaced with a brand-new part

I don’t think it is any of the door status switches causing the BCU to wake up randomly when the car is off as I would imagine that the interior lights would come on if that was the case?

Below are the things that I have checked so far:

• Navigation computer in the boot – I have tried disconnecting all the cables to all modules in the AV compartment in the boot.
• There are no signs of water ingress in the AV or fuse compartment in the boot.
• The headlight wiper fuse has been removed.
• The bonnet switch has been replaced with a brand-new part – not that is was playing-up before but it was a cheap part so I replaced it just to be sure.
• I have checked all the fuses in the glovebox and boot (checked relays in the boot area, too).
• I have tried removing the following fuses (separately) and the issue still occurred – 11, 12, 17, 18, 24, 25, 27, 31, 39, 41, 43, 58 and 86.
• I’ve read a few posts about the FSR causing battery drain; however, this is usually accompanied by issues with the blower speed control and the blower continuing to run after the car has been turned off – I don’t have any of these issues so I have discounted it being the cause.
• I have tried disconnecting the battery for several hours and touching the positive and negative cables to reset everything.

Removing fuse 27 did seem to stop the battery drain but I was told that was probably because that fuse powers the BCU so it obviously wouldn't have been able to keep waking up and subsequently draining the battery. I couldn't tell if removing that fuse had any impact on the BCU waking up as it also covers interior lights (including the PRND lights) so I don't know if it was still waking up randomly.

The car has no modifications at all – everything is completely stock.

Apart from this, there are absolutely no other issues with the car – everything works perfectly and the car drives beautifully.

Any assistance or advice on this issue would be greatly appreciated! I've spent countless hours researching this issue and trying different things but I just can't find a solution.
 

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2006-2009 Range Rover MkIII / L322
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RF interference could be causing it. Do you live anywhere near an airport, cell tower or the like, if so you may be getting interference that the locking system sees as a door lock or unlock signal and it leads to the BCU waking up in preparation for someone opening the doors.
 

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Australian spec car would have the fob and receiver operating on 433 MHz so the sort of things that cause problem in the US are different elsewhere (as US fobs operate on 315 MHz). 433 MHz is used for numerous different low power devices, wireless doorbells, weather stations, garage door openers, wireless burglar alarms, wireless central heating controllers, etc. I had a problem with a faulty central heating controller that was causing a P38 to do similar things. If a door was left open every couple of minutes the dash would beep and display interior lights off, interior lights on, interior lights off and so on. Have you recently added any new home electronics?
 

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Discussion Starter #4
Hi Guys,

Thanks for the replies - I really appreciate the advice.

I haven't recently installed any new wireless electronics at home. The issue seems to occur at different places, too. I frequently take the car to my family's rural property which is quite remote and doesn't have any wireless electronics (except mobile signal and 4G, etc.) and the same issue occurs.
 
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