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2018 G80 Battery Drain Mystery - Dies overnight even with new battery!

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Mike T. · rep 0 · May 25, 4:37 AM · 1 replies · solved · Question

Vehicle: 2018 Genesis G80 3.8L

Hey everyone,

I'm having a super frustrating issue with my 2018 Genesis G80 3.8L. For the past few weeks, the battery keeps dying overnight. I've replaced the battery twice now, thinking it was just a bad cell, but the problem persists. Each morning, it's completely dead.

I've checked for obvious lights left on, but everything seems fine. Could this be a parasitic draw? I'm not sure where to even start looking. It's really inconvenient, especially when I have to be somewhere early. Has anyone else experienced something similar with their G80 or other Genesis models?

Any advice on how to diagnose this or common culprits would be greatly appreciated before I take it to the dealership.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:37 AM

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ClearTheCode admin answer:

A persistent battery drain, even with a new battery, almost always indicates a parasitic draw. This means something is continuously drawing power from the battery even when the vehicle is off and locked. Diagnosing this can be tricky but is essential to resolve the issue.

Causes of Parasitic Draw:

  1. Faulty Modules: Common culprits include infotainment systems, telematics units, door lock actuators, or even a faulty alternator diode that allows current to flow backward.
  2. Aftermarket Accessories: Non-factory installed alarms, stereo systems, or dash cams can sometimes be wired incorrectly or develop faults.
  3. Stuck Relays: A relay that remains energized when it shouldn't can keep a circuit active.
  4. Wiring Issues: Short circuits or chafed wires can cause unintended current paths.

When to See a Shop:

If you're not comfortable performing electrical diagnostics, or if initial checks don't reveal the problem, it's best to consult a professional Genesis service center or a qualified automotive electrician. They have specialized tools and diagnostic procedures to pinpoint the exact source of the draw.

DIY Diagnostic Steps (Basic):

  1. Check for Obvious Culprits: Ensure all interior lights, trunk lights, glove box lights, and vanity mirror lights are off. Confirm no phone chargers or accessories are left plugged in.
  2. Perform a Parasitic Draw Test:
    • Connect a multimeter in series between the negative battery post and the negative battery cable. Ensure the vehicle is off, doors are closed (you might need to trick the latch), and all accessories are off.
    • Wait at least 15-30 minutes for all modules to 'go to sleep.' The draw should ideally be under 50 milliamps (0.05 amps) for most modern vehicles.
    • If the draw is too high, start pulling fuses one by one while monitoring the multimeter. When the amperage drops significantly, you've identified the circuit causing the draw. This narrows down the problem area considerably.

OBD Codes:

Parasitic draws typically do not trigger specific OBD-II diagnostic trouble codes (DTCs) directly, as the vehicle's computer is usually off. However, if a module is failing and staying awake, it might log a 'U' code (network communication fault) or a 'B' code (body electrical fault) that could provide a hint. A professional scan tool can check for these deeper module-specific codes.

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