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.

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.

Take it back to the people who fitted the new BCU and get them to check it over
Let us assume they coded it correctly to the car ?

The car will periodically wake itself up and do some self levelling, any signs of this happening

Does the problem go away if you disconnect the BCU ? .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

I do need to go back to the LR specialist auto electrician who fitted the BCU because the front parking sensors stopped working after it was replaced. I assume this is something that may need to be re-enabled. I'll get him to check the BCU again. He said that he just copied the config of the old BCU when he programmed the new one.

I haven't tried disconnecting the BCU entirely but I did remove Fuse 27 before I parked the car for an extended amount of time and when I next started it (over a week later) the car started perfectly. I read that Fuse 27 has something to do with the BCU but I can't tell if it makes any difference to the BCU waking up as it also covers the interior lights so the PRND lights stop working when it is removed.

I did read something about the periodic checks and self-levelling but because the BCU wakes up so frequently I didn't think that would be it.

I have a feeling that this issue was occurring before the BCU was replaced, though. I remember that interior lights turning back on issue I mentioned happening since I've owned the car (almost 2 years). I used to be able to leave the car for weeks without the battery draining, though. Perhaps that is just because the battery is starting to fail because it has been completely discharged so many times because of this issue.

Did you resolve this issue?

There wa# a problem with the alarm receiver some years back. It was receiving signals from any device on 433MHz and waking the BCU up, which woke everything else up and flattened the battery.

433MHz is used widely in household non-licensed products I.e remote controls, weather stations, alarm systems. LR superseded the original receiver with one that had tighter tolerances, so was not so susceptible.

What I can’t remember is what model years were affected.

Yep, I did end up solving this issue. It actually turned out to be the brand-new BCU - it was faulty. I put the old BCU back in and everything is back to normal. The power steering and rear doors not unlocking issue came back but I found a repair service for that exact issue on eBay. I sent the original BCU off for the repair, got it back within a few days, fitted and everything is perfect.
Hope this helps!

Nice. Thanks for updating

I have a battery drain and notice my bcu keeps waking up.
I had an ammeter connected up last night with the door tricked into thinking it is shut, bonnet switch disconnected, interior sensor disabled and every few minutes the light by the gear selector would come on and the little fan behind the HEVAC unit would start and the satnav night sometimes came back on.
I started pulling fuses until I set the alarm off at 10 pm and couldn’t shut it off.
Something keeps waking it up...
Do you have the same problem as OP?