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2018 Outback Battery Draining Overnight - Help!

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Chris P. · rep 0 · May 22, 3:16 AM · 1 replies · solved · Question

Vehicle: 2018 Subaru Outback 2.5i Limited

Hey everyone,

I'm having a really frustrating issue with my 2018 Subaru Outback 2.5i Limited. The battery keeps dying overnight, almost every other day. I've already replaced the battery with a brand new one, thinking that was the problem, but it's still happening.

I've checked the obvious things like making sure all lights are off and doors are closed properly. There are no aftermarket accessories installed, just the factory setup. It's really inconvenient, especially when I need to get to work.

Has anyone experienced a similar parasitic draw issue with their Outback? What should I be looking for? Any advice on how to diagnose this would be greatly appreciated.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:16 AM

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ClearTheCode admin answer:

Battery draining overnight, even with a new battery, almost always points to a parasitic draw. This means something in your 2018 Subaru Outback is consuming power even when the vehicle is turned off.

Common Causes:

  1. Stuck Relays: A relay that doesn't fully disengage can keep a circuit active.
  2. Faulty Modules: Infotainment systems, body control modules (BCM), or other electronic control units (ECUs) can sometimes fail to enter 'sleep' mode.
  3. Glove Box/Trunk Lights: These small lights can sometimes stay on due to a faulty switch, unnoticed.
  4. Aftermarket Accessories: Although you mentioned none, even a poorly installed dash cam or USB charger could cause a draw.
  5. Corrosion/Shorts: Damaged wiring or corrosion can create unintended electrical paths.

Troubleshooting Steps:

  1. Perform a Parasitic Draw Test:
    • Connect a multimeter in series between the negative battery post and the negative battery cable. Set the multimeter to measure amperage (A or mA).
    • Ensure all doors are closed, lights are off, and the car has been 'asleep' for at least 15-30 minutes (some modules take time to power down).
    • A normal draw should be around 20-50 mA. Anything significantly higher indicates a problem.
  2. Pull Fuses: While monitoring the multimeter, systematically pull one fuse at a time from both the under-hood and interior fuse boxes. When the amperage drops significantly, you've identified the circuit causing the draw. This helps narrow down the faulty component.
  3. Check for Visible Lights: Double-check glove box, trunk, and under-hood lights for proper operation.

When to See a Shop:

If you've performed the parasitic draw test and identified a high draw but can't pinpoint the exact component after pulling fuses, or if the draw is intermittent, it's best to take your Outback to a qualified Subaru technician. Diagnosing complex electrical issues, especially those involving control modules, requires specialized tools and expertise. They can use advanced diagnostic equipment to identify the specific module or component that isn't shutting down correctly.

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