2016 Legacy battery parasitic drain

[Duboisly]

I have a 2016 legacy 2.5 limited. I have a battery drain / parasitic load issue. As of September 2021 I've replaced 3 batteries and about to put my 4th in. I did a drain check and on Fuse 9 under hood/main fuse box I get 0.6 amp drain then when i pull the fuse it drops to 0.06 amps. This feeds the data communication module / DCM. I haven't troubleshot it more from there.
How long does it take for the DCM to go to sleep mode?
Also has anyone changed out a DCM, how tough is it?
Per the manual it looks like you have to pair the unit to the car, can that be done by a DIY person?

 

[Retired Engineer]

Have a parasitic drain on my Mercedes, can't find it. Installed inexpensive battery disconnect on Negative pole of battery, problem solved. You may wish to use disconnect that operates from cable to dashboard. Also nice theft protection. Drawback is your DCM will need a few miles to "re-learn" tuning parameters. I can't even notice this.
If this "hard Reset" doesn't correct the present Subaru DCM, isolate it from power, and then mine is a plug-in exchange for new one. Then same "learning curve" occurs as you drive it first time, this should "pair it to the car."

Noticed you'e replaced three batteries while troubleshooting. Subarus are noted for their relatively small batteries
(possibly to reduce weight), and then of course automobile batteries are not able to be fully recharged after being fully drained. I swapped in a same Group 24 deep cycle marine battery. Wow! Huge improvement. Cost me $88
exchange for my dying "5 year" Interstate, on the way out at 3 1/2 years. You'll need to remove battery tray to accommodate deeper height of an inch or so, and don't forget to re-install black plastic heat shield. May need to buy one longer battery cable. I found an Advance Auto Parts store close to a lake, so it stocked lots of marine batteries.
Hope this helps.

 

[dmakris]

Have a parasitic drain on my Mercedes, can't find it. Installed inexpensive battery disconnect on Negative pole of battery, problem solved. You may wish to use disconnect that operates from cable to dashboard. Also nice theft protection. Drawback is your DCM will need a few miles to "re-learn" tuning parameters. I can't even notice this.
If this "hard Reset" doesn't correct the present Subaru DCM, isolate it from power, and then mine is a plug-in exchange for new one. Then same "learning curve" occurs as you drive it first time, this should "pair it to the car."

Noticed you'e replaced three batteries while troubleshooting. Subarus are noted for their relatively small batteries
(possibly to reduce weight), and then of course automobile batteries are not able to be fully recharged after being fully drained. I swapped in a same Group 24 deep cycle marine battery. Wow! Huge improvement. Cost me $88
exchange for my dying "5 year" Interstate, on the way out at 3 1/2 years. You'll need to remove battery tray to accommodate deeper height of an inch or so, and don't forget to re-install black plastic heat shield. May need to buy one longer battery cable. I found an Advance Auto Parts store close to a lake, so it stocked lots of marine batteries.
Hope this helps.

...or you could identify the root cause of the drain - I just posted diagnostic steps that worked for me under 2017 Outback battery drain topic: https://www.thesubaruforums.com/posts/65841/

 

[Duboisly]

Update: Subaru recently sent me a letter that the DCM will cause some of the same issues now that 3g is no longer available. DCM does not go into sleep mode.

 

[Erp]

Subaru says there are no DCM replacements till 2025. They have a bypass box that will fix the drain. I'm having one installed on 5-22-2024. I have a 2019 Legacy.
I got the letter also, but had already complained.
If you remove the #10... 7.5 amp fuse your battery won't drain. See pic. You will only have rear radio speakers working.
Try it. Get into the dealer asap. Should be a bunch showing up. Save the fuse and put it back in before you go to the dealer for the repair. See the pic. Red dots on fuse to remove.
PS they made me an appointment to replace it, but then when I showed up they wouldn't do anything till they proved to themselves I had the drain. They did which I already knew after two batteries. Then they ordered a part to fix the problem. Now a week later I will have it fixed hopefully. I drove 120 miles for them to prove it, and now I will drive another 120 miles round trip to get it fixed. Great customer service.
Under the hood look under the fuse plastic cover over fuse box and you will see the fuse. Says 7.5 DCM

 

[Duboisly]

Subaru says there are no DCM replacements till 2025. They have a bypass box that will fix the drain. I'm having one installed on 5-22-2024. I have a 2019 Legacy.
I got the letter also, but had already complained.
If you remove the #10... 7.5 amp fuse your battery won't drain. See pic. You will only have rear radio speakers working.
Try it. Get into the dealer asap. Should be a bunch showing up. Save the fuse and put it back in before you go to the dealer for the repair. See the pic. Red dots on fuse to remove.
PS they made me an appointment to replace it, but then when I showed up they wouldn't do anything till they proved to themselves I had the drain. They did which I already knew after two batteries. Then they ordered a part to fix the problem. Now a week later I will have it fixed hopefully. I drove 120 miles for them to prove it, and now I will drive another 120 miles round trip to get it fixed. Great customer service.
Under the hood look under the fuse plastic cover over fuse box and you will see the fuse. Says 7.5 DCM

I took mine in a couple of weeks ago. They said my average battery drain was under their limit of ~70 milliamps.. Mine bounces below and above 70 milliamps. They wouldn't replace my DCM. The did a battery test and tried to charge me for it, I protested and they waived the charge. They stated my battery needed to be replaced. It's only 2-1/2 years old. I did a test with my meter and the battery is at 50% of life. The battery has about 45 amp hours per nameplate. If/when I change the battery I'm going big. I found a deep cycle battery with ~100 amp-hours and more cold cranking amps that will fit in my battery bay (with some slight modifications).