Battery drain... is it the BCU or LSM?
 

Hello everybody.
Something went wrong with my other topic. I think I didn't save it properly, because I can't find it anywhere :(.

Nonetheless, the situation is basically that I had some trouble with an empty batter last december. It was discharging very quickly. I thought it was the batteries fault, so I replaced it with a new one. That went well for a few months, but started acting up again around March. Seeing as it has become worse, and I have to recharge the battery at least once a week, even thought the car isn't being used, I thought i'd best get my multimeter out.

The problem is that the battery has a drainage of roughly 0.43 amps. All the time. This has drained the battery a few times, slowly killing it. The battery is there fore due to be replaced (again), but I want to find the problem first.

The things I've checked so far:

- The alternator gives 14.4 at idle and 14.2 with every single thing in the car turned on, and at max settings
- Battery gives roughly 12.5 volts when it is charged and after 48 hours without anything connected to it, goes to 11.5 volt (it'll be replaced, I know this one is kinda broken now)
- I removed every single fuse in the engine compartment, together with all the relays. The amps stayed at 0.43/0.42, except when taking out the 50 amp fuse just below the master fuse (the really big one). Taking this out, makes it drop to 0.05 roughly.
- I disconnected the alternator and all the interior lights. This made zero difference.
- I cleaned up the earth-to-body connection just below the battery case (no difference)

I then put everything back in the engine bay, and went to the interior.

- I removed every single fuse in the interior. The best I got was a drop to 0.38 amps when pulling fuse 5 and also when pulling fuse 22 I believe. The others didn't do anything. I put all fuses back after being done.
- I disconnected the subwoofer, the Navall unit, the diming rearview mirror and the dashcam. Stil at 0.43 amps.

I then put everything back again.

- I removed the LSM and it went down to 0.38 amps
- I then also removed the BCU and it went down to 0.03 amps
- I then reconnected the LSM, but didn't connect the BCU which gave me 0.03 amps.

Vinnie, check to see if the background illumination on the LSM is lit at night with the car locked, I've see this fault quite often now and it prevents the BCU from going to sleep.

The quiescent current draw is circa 45mA (0.045A) under normal conditions after the BCU enters standby mode ;)

Brian :D

Good point, forgot to mention that I did the towel test haha. Towel over my head and then inspect if the lights go off. Luckily, as soon as I take out the key, the lights go off.

Different qeustion, could a bluetooth obd connector keep the BCU or LSM alive? I forgot to check that one and it just pops in my head.

What I would say is if it is Bluetooth type OBD device it will constantly pull power to broadcast a signal. Whether that will drain the battery depends on how often you drive it I guess. Funny enough I came across this on a smart car a while back but the owner wasn’t using the car often.
Mick

Well, tested the Bluetooth dongle a few times, and it gave me a max drop from 0.43 amps down to 0.38 amps. Not enough, but still good to know.

I am now testing the bcu and lsm again, and leaving a minimum of 1 hour in between. Disconnect the one, connect the other, wait and measure. As far as I've gotten right now, I am still very much looking at the BCU being the culprit.

Would anybody know if a BCU can cause this problem? Or does it need to be something that is connected to the BCU, but is not wired in on a fuse?

Well, the last few days have been a matter of testing to see if I could find something more. I simply wanted to test whether it was the LSM or the BCU.

So I disconnected the one, connected the other and measure the usage 1 hour later. To make sure, I repeated the whole test 3 times.

Friday:
- Without BCU, but with LSM = 0.03 amps
- Without BCU and without LSM = 0.03 amps
- With BCU, but without LSM = 0.38 amps
- With BCU and with LSM = 0.34 amps

After this test, I removed the Bluetooth ODB dongle (I forgot about it... 　 )

Saturday (waited 2 hours between each test):
- Without BCU, but with LSM = 0.00 amps (meter would show 0.03 and then drop to 0)
- Without BCU and without LSM = 0.00 amps (meter would show 0.03 and then drop to 0)
- With BCU, but without LSM = 0.34 amps
- With BCU and with LSM = 0.31 amps

Sunday (waited almost 3 hours between each test):
- Without BCU, but with LSM = 0.00 amps (meter would show 0.02 and drop to 0)
- Without BCU and without LSM = 0.00 amps (meter would show 0.01 and then drop to 0)
- With BCU, but without LSM = 0.07 amps
- With BCU and with LSM = 0.31 amps

I don't understand why sunday was different to saturday...

All tests where done with the doors closed for at least an hour and a clamp on the bonnet switch. Immediately after opening a door the amps would go up to 0.34 amps, except when the BCU and LSM was removed. It seems the car doesn't know when the door is open without the BCU??

From what I'm seeing at the above, I'd start to think that the BCU is the issue. How can I test this any further??

I was asked to look at a strange current drain, but everytime I looked at the car it behaved as it should do (next to no current drain) at some point later the owner changed the drivers door lock and has had no issues since, so all I can think is the door was occasionally not signalling closed properly. Perhaps no help, but may be worth just checking the interior lights are going out as expected and horn is not beeping when locking

That is another good point you just raised; I know the car used to horn if any door is open. But it doesn't do this anymore.
The doors lock fine, and the alarm doesn't go off (no extra blinking lights when unlocking the car), but it doesn't honk when I try to lock the car with the boot open.

Taking a few fuses out each time, and waiting for 2 hours gave me enough information to know that fuse F36, F35, F34, F33 and F32 should be the culprits.

Now its a matter of putting them back one at a time, to see which one causes the problem.

As far as I can tell:
F36 = Alternator??
F35 = Heated side mirrors
F34 = (unknown, something with the engine?)
F33 = Something with frost, and the seatbelt?
F32 = Something with TC and ABS?

This may help.