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Old 11-07-2023, 01:43 PM   #1
Fast03Wagon
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Default New to me STI - Battery Drain?

Hi,

I've got a new to me 2019 STI as more of a hobby car at the moment, still driving my Outback more often.

I let the STI sit for about a week in the garage and the battery was dead when I went to start it. Do I have a battery drain, or do these newer cars and their electronics need to be driven more often than once a week to charge the battery? If so, sounds like I need to use a trickle charger.

I feel like a week is not that long to drain the battery completely but maybe so..

Thanks!
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Old 11-07-2023, 02:08 PM   #2
Mulder
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Should last more than a week if the battery is fully charged to begin with.
First thing to do since you just got the car is to charge the battery and have it tested, it could just be weak after 4+ years.
If there is still drain with a known good battery you can do a parasitic drain test by connecting an ammeter in series with one of the battery terminals. After allowing time for everything to go into standby mode the drain shouldn't be more than about 50ma or so. If it's much higher you'll need to do some troubleshooting to find where the excess drain is. Start with obvious stuff like the trunk light.
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Old 11-08-2023, 05:18 PM   #3
Fast03Wagon
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Quote:
Originally Posted by Mulder View Post
Should last more than a week if the battery is fully charged to begin with.
First thing to do since you just got the car is to charge the battery and have it tested, it could just be weak after 4+ years.
If there is still drain with a known good battery you can do a parasitic drain test by connecting an ammeter in series with one of the battery terminals. After allowing time for everything to go into standby mode the drain shouldn't be more than about 50ma or so. If it's much higher you'll need to do some troubleshooting to find where the excess drain is. Start with obvious stuff like the trunk light.
Thanks! I'll do some digging this weekend.
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Old 11-08-2023, 07:02 PM   #4
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Do you pay for Starlink? I'll assume no because nobody does. There is a fuse in the engine compartment called DCM. Pull it and put it with your spare fuses. This is a common problem with Subarus because the Data Communications Module spikes current once a second, always. This fuse feeds nothing else. Even if this isn't the problem, it's a problem.
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Old 11-09-2023, 09:14 AM   #5
Fast03Wagon
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Quote:
Originally Posted by Jack View Post
Do you pay for Starlink? I'll assume no because nobody does. There is a fuse in the engine compartment called DCM. Pull it and put it with your spare fuses. This is a common problem with Subarus because the Data Communications Module spikes current once a second, always. This fuse feeds nothing else. Even if this isn't the problem, it's a problem.
Awesome, I will definitely pull this. Thanks!
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Old 11-13-2023, 09:36 AM   #6
Fast03Wagon
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Quote:
Originally Posted by Jack View Post
Do you pay for Starlink? I'll assume no because nobody does. There is a fuse in the engine compartment called DCM. Pull it and put it with your spare fuses. This is a common problem with Subarus because the Data Communications Module spikes current once a second, always. This fuse feeds nothing else. Even if this isn't the problem, it's a problem.
Unfortunately, pulling that fuse also kills the dash speakers and makes the audio pretty bad.

Either way, thanks for alerting me to this - it sounds like a known issue but no real fix except for having a dealer perform an update. I'll explore that route.
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Old 11-13-2023, 05:01 PM   #7
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Quote:
Originally Posted by Fast03Wagon View Post
Unfortunately, pulling that fuse also kills the dash speakers and makes the audio pretty bad.

Either way, thanks for alerting me to this - it sounds like a known issue but no real fix except for having a dealer perform an update. I'll explore that route.
Interesting. I did this following a South Main Auto youtube video. But he was doing a 2017 Subaru Legacy and that's what my wife has. Perhaps find the Data Communications Module and unplug it. I have no idea where it is. In the video, he found in the wiring diagram that in the Legacy, nothing else was tied to that fuse. I'll have to see what happens in my son's STi. I did it in my 19 Crosstrek and it's been fine.
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Old 11-13-2023, 08:43 PM   #8
Fast03Wagon
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Quote:
Originally Posted by Mulder View Post
Should last more than a week if the battery is fully charged to begin with.
First thing to do since you just got the car is to charge the battery and have it tested, it could just be weak after 4+ years.
If there is still drain with a known good battery you can do a parasitic drain test by connecting an ammeter in series with one of the battery terminals. After allowing time for everything to go into standby mode the drain shouldn't be more than about 50ma or so. If it's much higher you'll need to do some troubleshooting to find where the excess drain is. Start with obvious stuff like the trunk light.
I disconnected the negative battery clamp and put one contact of my multimeter on the disconnected clamp and the other contact on the negative terminal of the battery and measured 7.5mA. So this points to me to the battery as the issue, since that's significantly less than you suggested the limit should be. I'll take it in and have it tested. Thanks for the input!

Last edited by Fast03Wagon; 11-13-2023 at 08:44 PM. Reason: spelling
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Old 11-13-2023, 08:50 PM   #9
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A lower drain is good. I gave 50ma as a somewhat arbitrary number for what would be considered nominal, with a much higher value being cause for concern.
Still a good idea to get the battery tested so you can rule it in or out as a potential cause for the drain.
It's also possible that the drain isn't constant and goes higher at times for things like what Jack mentioned or something else. But, without a way to record the current over time it's hard to tell.
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Old 12-03-2023, 09:55 PM   #10
Brentpierce
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Hope its just the battery getting weaker.
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Old 12-04-2023, 06:59 AM   #11
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Quote:
Originally Posted by Fast03Wagon View Post
I disconnected the negative battery clamp and put one contact of my multimeter on the disconnected clamp and the other contact on the negative terminal of the battery and measured 7.5mA. So this points to me to the battery as the issue, since that's significantly less than you suggested the limit should be. I'll take it in and have it tested. Thanks for the input!
You performed the test incorrectly. All modules need to go to sleep before you take the reading. You need to disconnect the terminals, place the ammeter between the terminals. Connect a jumper between the disconnected terminals (across the ammeter connections). Then you let the vehicle set for 5-10 minutes to allow all the electronics modules to "go to sleep". After that remove the jumper and check the ammeter. Subaru specifies no more than 70 mA (0.070A) You will see an occasional blip as mention.

BTW: Unplugging the DCM will kill the front speakers as well - the front speakers are wired from the radio through the DCM.
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Old 12-04-2023, 08:18 AM   #12
Mulder
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Elbert is correct, I should have mentioned that step.
However the drain will generally be higher initially until everything goes to sleep, so if you did actually see 7.5ma upon connection it's probably ok. You could certainly repeat the test again and use the stated procedure.
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Old 12-04-2023, 05:08 PM   #13
Nickdalessandro
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Anyone know how to fix this problem on a 17 sti, there is no dcm or telematics fuse listed in the manual? I've also had the battery tested and its fine.
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Old 12-04-2023, 05:49 PM   #14
Elbert Bass
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Quote:
Originally Posted by Nickdalessandro View Post
Anyone know how to fix this problem on a 17 sti, there is no dcm or telematics fuse listed in the manual? I've also had the battery tested and its fine.
You would be amazed how many times I would find the trunk/cargo lamp turned on in cars that came in for a persistent battery drain...
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Old 01-30-2024, 03:21 PM   #15
Pearlwo
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Please tell me, could the battery have failed within two years? Since I replaced it, it discharged completely once but worked after charging. Lately, if I don't drive for at least 3-4 days, it starts as if it's severely discharged for the first time. I suspect there's a discharge, but I haven't figured out where yet.
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Old 02-20-2024, 09:33 AM   #16
Fast03Wagon
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To update this thread, I bypassed the DCM unit with this:

https://www.autoharnesshouse.com/69018.html

It solved the battery issues for me and keeps the front speakers and microphone working. Now I can start the car after a week+ of sitting in the garage no problem.
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Old 02-21-2024, 09:03 AM   #17
Charlie-III
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Quote:
Originally Posted by Fast03Wagon View Post
To update this thread, I bypassed the DCM unit with this:

https://www.autoharnesshouse.com/69018.html

It solved the battery issues for me and keeps the front speakers and microphone working. Now I can start the car after a week+ of sitting in the garage no problem.
Hey, thanks for the update, I hate dead end threads.
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Old 03-05-2024, 10:16 PM   #18
21ej
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I have a '21 and my battery will also die after letting the car sit for 1-2 weeks. Not sure if its a normal thing. Seems like it's rather quick for it to die
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