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2018 Outback Touring: Persistent Battery Drain Issues - Dead Battery After A Few Days

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Sarah K. · rep 0 · May 22, 3:18 AM · 1 replies · solved · Question

Vehicle: 2018 Subaru Outback Touring

Hey everyone, I'm having a really frustrating issue with my 2018 Subaru Outback Touring. For the past few weeks, if I leave it parked for more than two or three days, the battery is completely dead. I've had to jump-start it multiple times.

I've already replaced the battery once, thinking it was just old, but the problem persists. I don't have any aftermarket electronics installed, and I'm pretty careful about turning off lights and accessories. Could this be a parasitic draw, and if so, what's the best way to track it down? It's really inconvenient and I'm worried about damaging the electrical system.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:18 AM

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ClearTheCode admin answer:

Persistent battery drain, also known as a parasitic draw, is a common issue that can be tricky to diagnose. It means something in your 2018 Subaru Outback Touring is drawing power even when the vehicle is off. Here’s how to approach it:

  1. Initial Checks:

    • Battery Health: Even if new, ensure the battery itself is good and fully charged. Have it load tested at an auto parts store. Also, check the battery terminals for corrosion and ensure they are tightly secured.
    • Charging System: Verify your alternator is charging the battery correctly when the engine is running. A failing alternator can lead to a constantly undercharged battery.

  2. Common Causes of Parasitic Draw:

    • Interior Lights: Dome lights, glove box lights, or trunk lights that aren't turning off completely.
    • Aftermarket Accessories: While you mentioned none, sometimes even a dash cam or USB charger left plugged in can draw power.
    • Infotainment System: A module that isn't properly shutting down.
    • Relays: A stuck relay can keep a circuit active.
    • Faulty Modules: Issues with the Body Control Module (BCM), keyless entry module, or other electronic components.

  3. Diagnosing a Parasitic Draw (DIY with a Multimeter):

    • Connect Multimeter: With the car off and all doors closed (or latches simulated), disconnect the negative battery terminal. Connect a multimeter in series between the negative battery post and the disconnected negative battery cable. Set the multimeter to measure amps (A or mA).
    • Wait for Sleep Mode: Modern cars can take 15-30 minutes for all modules to 'go to sleep.' The draw should drop to below 50mA (0.05A). If it's significantly higher, you have a draw.
    • Pull Fuses: Systematically pull one fuse at a time from the fuse box (both under the hood and inside the cabin) while watching the multimeter. When the amperage drops significantly, you've found the circuit with the draw.

When to See a Shop: If you're uncomfortable performing these diagnostic steps, or if you've identified a circuit but can't pinpoint the exact component (e.g., the 'radio' fuse reduces the draw, but you don't know if it's the head unit or an antenna amplifier), it's best to take your Subaru to a qualified technician. They have specialized tools and diagnostic software to identify module failures or complex wiring issues. They can also check for any stored diagnostic trouble codes (DTCs) related to low voltage, even if a Check Engine Light isn't on.

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