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

Supervinnie40 · 29th May 2020, 14:55

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.

29th May 2020, 14:55	#1
Supervinnie40 I really should get out more....... Rover 75 1.8 Club Join Date: Dec 2013 Location: Tilburg (Netherland) Posts: 2,615 Thanks: 572 Thanked 336 Times in 247 Posts	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. __________________ Proud owner of the Dutch "Golden 75". A much loved Gold White Metallic Rover 75 1.8 na from 2000.