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Hi, just wondering if any of you may of experienced battery drain overnight? My Forester gets below 12V every day.
I did the Subaru dark current drain test and its around 2.2 AMPS! nowhere near the max allowed 70 MA..
I have no other external devices etc other than dash cams with park mode but I disconnected that and it made no difference.
The draw is related to the 30 AMP "backup" fuse as removing this drops the drain right down close to zero. Watching it on analogue meter I can see it drop sometimes (not to zero) and when it does I can make it go back up by removing and installing the backup fuse. It almost seems like some sort of capacitor. Any tips at all on this one?? Thanks Dick

G’day Dick,

Being a 2022 model, isn’t it still under warranty? I know that can be a painful process but since it’s the backup power circuit fuse that when removed stops the drain I’m out of ideas without looking at a wiring schematic for your model.

Can you tell us what the back up power fuse supplies power to? Usually the back up power is associated with the ECU in older models.

I look forward to hearing what you find out about this circuit.

Cheers

Bennie

Hi, yes its under warranty but I cant get it there for another 5 or so weeks due to medical treatment.. My aim was to do some prelim checks to see if I could locate the drain.
Pulling backup fuse disables the security and door opening etc, so couldnt get on the check other items, assume is the BCM as well. Will try with doors open next.
I read about pulling the DCM fuse to help with drain but it did nothing and everything still works.
I intend to use thermal gun to try and find component that is warmer, does anybody know where the BCM is on this model please?
I can pick up the backup fuse its .5 warmer.

That’s fair enough with wanting to do a prelim check.

If the backup fuse is also responsible for the interior lights, is there one that’s staying on all the time? I’m wondering if there’s one in a door jamb that’s on that you can’t see.

I like the idea of the heat gun but I think accessing all the modules will be the logistical nightmare that kills this idea ;(

Sorry I can’t be of more help.

Cheers

Bennie

My troubleshooting of drain was correct, it was the power supply unit for front and rear cameras. They replaced it with an "updated" unit, battery now hangs on after several days. Still down to 12.2 ish but no lower and it starts ok.
The Suby dark current test is easy to do if you suspect a drain..

I’m glad to hear that you found the issue and had it resolved!

Thanks for sharing the fix!

Cheers

Bennie

You might have to get something like a CTEK MXS 5.0 charger, to top off the battery every 3 - 4 weeks (just a guess) to keep it in top condition.