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2018 Sierra 1500 Battery Drain & P0562 Code

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Mike T. · rep 0 · May 25, 2:39 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

Hey everyone,

I've been having a frustrating issue with my 2018 GMC Sierra 1500 SLT. For the past few weeks, the battery seems to drain overnight, leaving me with a slow crank or sometimes a completely dead battery in the morning. I've had to jump-start it more times than I can count.

The check engine light also came on, and when I scanned it, I got a P0562 code, which points to 'System Voltage Low'. I replaced the battery about 6 months ago, so I'm hoping it's not that again. Could it be the alternator, or something else drawing power when the truck is off?

Any insights or similar experiences with a 2018 Sierra would be greatly appreciated before I take it to the shop. Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:39 AM

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ClearTheCode admin answer:

The P0562 code ('System Voltage Low') on your 2018 GMC Sierra 1500 SLT indicates the Powertrain Control Module (PCM) detected that the system voltage was below a specified limit for a set period. This aligns perfectly with your reported battery drain issues.

Here are the common causes and diagnostic steps:

  1. Check Battery Health: Even if it's relatively new, a faulty cell or improper installation can cause issues. Have it professionally tested for CCA (Cold Cranking Amps) and overall health.
  2. Inspect Alternator Output: The alternator is responsible for charging the battery and powering the electrical system while the engine runs. A failing alternator won't charge the battery properly, leading to low voltage. Test its output voltage and current under load.
  3. Diagnose Parasitic Draw: This is a common culprit for overnight battery drain. Something is staying on or drawing power when the vehicle is off. This can be tricky to find but often involves:
    • Using a multimeter to measure current draw after the vehicle has 'gone to sleep' (typically 30-60 minutes after turning off).
    • Pulling fuses one by one to isolate the circuit causing the draw. Common culprits include aftermarket accessories, faulty modules (e.g., infotainment, BCM), or interior lights.
  4. Inspect Wiring and Connections: Loose, corroded, or damaged battery terminals, ground wires, or alternator wiring can cause voltage drops and charging issues. Ensure all connections are clean and tight.

When to See a Shop: If you're not comfortable performing electrical diagnostics, or if the issue persists after checking basic connections and battery health, it's best to take your Sierra to a qualified mechanic. Diagnosing parasitic draws can be time-consuming and requires specific tools and knowledge. They can pinpoint the exact cause of the P0562 code and the battery drain, preventing further electrical system damage.

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