Possible battery drain?

[TheGriffter]

Hi, long time lurker but regular reader now needing some assistance for a possible battery issue on my E53 3.0d Sport (2005/55), if people are able to offer some thoughts.

I have searched here and a number of places but seem to have a combination of things possibly contributing to the issue, hence starting a new topic. I have tried to post as much info as possible but apologies if this means it is lengthy....

6 weeks ago I reversed into a lampost and cracked (not smashed) the rear nearside light cluster, and knocked the rear bumper from its clips.

4 weeks ago I came out of work and the car unlocked with button on the fob as normal. However, the splash screen that normally comes on the sat nav did not appear. The car would not start although interior lights and dashboard lights worked. I tried to start it a few times and what charge was left in the battery finally went and even the internal/dash lights then went out.

The AA came and put a booster charge on via the jump post under the bonnet and got the car started and left it running for 20 mins. It then restarted under its own battery power. The voltages and currents were tested along with the alternator and all tested ok. The yellow "4 x 4" warning light stayed on whilst I drove home, but then disappeared the next morning when I used the car.

I put this flat/drained battery down to me or one of the kids leaving a door/light on begrudgingly as I am very careful about this.

Car has then been faultless until today...
Car would not respond to key fob at all, spare key was tried (thinking it may be the battery in key) - no difference.
I opened the drivers door manually with the key. Car would not start, no dashboard lights, no internal lights at all.
The AA dutifuly came and started the car again, checked the alternator, battery etc, all of which proved good.
The car was then restarted under its own steam, however, this time when started the fuel gauge, rev counter and instrument cluster lights did not come on at all!!

My searches have thrown up a few possibilities, including:

• Wheel / ABS sensor (hence my mentioning the reversing incident)
• Final stage resistor (I can't hear anything noticeably staying "on" after ignition is switched off)
• "Reset" the battery by taking out fuses 1, 43 and 45 (don't really understand this one!)

I am hoping the car will start tomorrow morning, the speedo/rev counter and fuel gauge will all start working and can book in with my local indy

Any thoughts based on my long story would be much appreciated

Cheers, Griff

[Thehinch]

I know this is going to sound random but the cause of my flat battery was the internal fan control unit. Its a module that sits up under the dashboard and controls the internal fan.  Mine had been coming on when the car was locked and draining the battery.  A symptom of this part failing was the dip in strength of the air blowing out of the vents. 

I to the same as you had the battery checked, the alternator checked, all interior and exterior lights were off and still the battery went flat.  How my mechanic found it in the end was he was sitting in the car with the doors locked scratching his head thinking about the issue and then apparently the fan came on. 

Hope you get the problem solved

[Mick.H]

Sounds like the "hedgehog" or official name "final stage resistor" issue that I had on my 5 series.
If replacing this make sure you go OEM as the cheaper ones are junk

[Thehinch]

Classic...hedgehog is a great name for it as it certainly looks like one. 

My mechanic now has a hedgehog burn on his forearm after accidentally leaning on it when he removed it.

[Mick.H]

Ouch

[TheGriffter]

Thanks for the swift replies - will definitely go OEM if replacing FSR is needed - quick update though...

Car started fine this morning, the speedo and temperature gauge worked fine, but no instrument readings on the cluster at all or warning lights appeared on normal startup, no rev counter at all and the fuel gauge started on zero and then suddenly jumped to past full during my journey to work!

Cheers, Griff

[Steamyrotter]

This happens a lot when batteries run flat.

You will need to disconnect the battery for approx 5 mins then re-connect
Should bring your cluster back to life..

[Colin]

Hi Griff , my battery drain problem was put down to a rear tailgate relay holding on , mechanic said there were two of them so he changed both, ( all done under warranty ) no problem since , good luck . Colin...

[TheGriffter]

Thank you everyone for the great advice.

I now have use back of the fuel gauge, rev counter and instrument cluster/display after disconnecting the battery for 5 mins and then reconnecting - thank you Steamyrotter - 

I now have a few possibilities as to the cause of the battery drain (FSR, rear tailgate relay). Is it better to get the car into my indy and get these monitored to see which is the culprit or just better to replace them?

The fault is intermittent so in theory the car could be with the garage for ages until the problem repeats itself

Thanks, Griff

[Steamyrotter]

Not a prob.  We're here to help.

Prob best to bite the bullet and replace the FSR anyway as if it is not faulty now, it will get there soon.....

[X5Sport]

Glad it worked.  The 'battery reset' is just about the standard fix for the X5 and usually the first thing the mechanics try.  If you do get the 4x4 warning light on, this is usually cleared by moving the steering all the way left and right to calibrate part of the system.  It's common when the battery is either flat or changed.

Richard