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2018 Outback Battery Draining Fast - Parasitic Draw?

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Mike T. · rep 0 · May 25, 2:16 AM · 1 replies · solved · Question

Vehicle: 2018 Subaru Outback 2.5i Limited

My 2018 Subaru Outback 2.5i Limited keeps having its battery die, especially if it sits for a couple of days. I've replaced the battery twice in the last year, and the alternator tests fine. It's really frustrating to come out to a dead car.

I've noticed sometimes the infotainment screen doesn't fully shut off, or maybe there's a light staying on somewhere I haven't seen. Could it be a module or something constantly drawing power?

I'm at my wit's end trying to figure this out. Any ideas on common culprits for parasitic draws in these models?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:16 AM

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ClearTheCode admin answer:

A persistent battery drain, especially after replacing the battery and confirming the alternator is good, strongly indicates a parasitic draw. This means something is drawing power even when the vehicle is off.

  1. Test for Parasitic Draw: You'll need a multimeter. Disconnect the negative battery terminal and connect the multimeter in series between the negative battery post and the negative battery cable. Set the multimeter to measure amps. After the car has been off for about 20-30 minutes (allowing modules to 'sleep'), the draw should ideally be below 50mA (0.05 amps). If it's significantly higher, you have a draw.
  2. Identify the Culprit Circuit: Once you confirm a draw, start pulling fuses one by one while monitoring the multimeter. When the amperage drops significantly, you've found the circuit causing the draw. Common culprits in Subarus can include:
    • Infotainment System: Head units that don't fully shut down or have internal faults.
    • Rear Gate Control Module: Known issues in some Outback models.
    • Interior Lights/Trunk Light: Sometimes a switch can stick or a bulb remains on.
    • Aftermarket Accessories: Anything wired directly to constant power without proper shut-off.
    • HVAC Blower Motor: Can sometimes run intermittently or stick.
  3. Check for OBD Codes: While parasitic draws don't always trigger specific codes, a faulty module causing the draw might log a communication error (U-code) or a power supply issue (B-code) that a professional scan tool could reveal.

When to See a Shop: If you're uncomfortable performing electrical tests or can't pinpoint the exact circuit, it's best to take your 2018 Outback to a qualified Subaru technician. They have advanced diagnostic tools and wiring diagrams to efficiently trace the draw and repair or replace the faulty component. Ignoring a parasitic draw can lead to premature battery failure and leave you stranded.

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