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2020 GMC Sierra 1500 - Mysterious Battery Drain Overnight

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Mike T. · rep 0 · May 24, 1:30 PM · 1 replies · solved · Question

Vehicle: 2020 GMC Sierra 1500 AT4

Hey everyone,

I'm having a really frustrating issue with my 2020 GMC Sierra 1500 AT4. For the past few weeks, if I leave it parked overnight, the battery is completely dead by morning. It's not just a little low; it's completely flat, won't even click.

I've had the battery tested, and it's good. The alternator also checks out fine. I'm suspecting some kind of parasitic draw, but I'm not sure where to even begin looking. It's really inconvenient having to jump-start it every single day.

Has anyone else experienced something similar with their Sierra or other GMC truck? Are there any common modules or components that are known to stay awake and drain the battery on these models? Any advice on how to track this down would be greatly appreciated before I take it to the dealership.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 24, 1:30 PM

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ClearTheCode admin answer:

Persistent battery drain, often called a parasitic draw, is a common and frustrating electrical issue. While your battery and alternator test good, something is consuming power even when the vehicle is off. Here's how to approach it:

  1. Check for Diagnostic Trouble Codes (DTCs): Even if the check engine light isn't on, a low battery can trigger codes related to voltage (e.g., P0562 for low system voltage) or specific modules that are failing to enter sleep mode. A scan tool can reveal these.
  2. Perform a Parasitic Draw Test: This is the most direct way to diagnose the issue.
    • Ensure all doors are closed, lights are off, and the key is out of the ignition.
    • Disconnect the negative battery terminal and connect a multimeter in series between the negative battery post and the negative battery cable (set to amperage, typically 10A or 20A range).
    • Wait for the vehicle's modules to 'sleep' (this can take 10-30 minutes on modern GMCs). A normal draw is usually under 50 milliamps (0.05 amps).
    • If the draw is high, start pulling fuses one by one from the fuse boxes (under the hood and inside the cabin) until the amperage drops significantly. This identifies the circuit causing the draw.
  3. Common Causes for Parasitic Draw in GMCs (2016-2026):
    • Infotainment System/Radio: Can sometimes fail to shut down completely.
    • Body Control Module (BCM): A faulty BCM can keep various systems awake.
    • OnStar Module: Known to occasionally cause drains.
    • HVAC Blower Motor Resistor: Can sometimes fail and draw power.
    • Aftermarket Accessories: Any non-factory installed items (dash cams, remote starters, sound systems) are prime suspects.
    • Door Ajar Switches/Hood Latch Switch: A faulty switch can trick the vehicle into thinking a door is open, preventing modules from sleeping.
    • Glove Box/Under Hood Lights: Ensure these are turning off.
  4. When to See a Shop: If you're uncomfortable performing electrical diagnostics, or if the parasitic draw test doesn't clearly point to a single fuse, it's best to take your Sierra to a qualified automotive electrical specialist or a GMC dealership. They have advanced diagnostic tools and wiring diagrams to pinpoint complex electrical issues. Ignoring a persistent drain can shorten battery life and potentially damage other electrical components over time.
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