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2018 Sierra 1500 SLT - Battery Draining & "Service Charging System" Warning

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Ryan M. · rep 0 · May 22, 3:43 AM · 1 replies · solved · Question

Vehicle: 2018 GMC Sierra 1500 SLT

Hey everyone,

I've been having a persistent issue with my 2018 GMC Sierra 1500 SLT. For the past few weeks, the battery seems to be draining overnight, and I'll often wake up to a dead truck. After jumping it, I sometimes get a "Service Charging System" message on the dash.

I've had the battery tested, and it seems okay, though it's the original. The alternator was also checked and passed. Could this be a parasitic draw, or something more serious with the charging system electronics? It's really frustrating to deal with, especially when I need to get to work.

Has anyone else experienced this with their Sierra? Any advice on what to check next before I take it to the dealership?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:43 AM

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ClearTheCode admin answer:

It sounds like you're dealing with a classic parasitic draw or an intermittent charging system fault on your 2018 GMC Sierra. While the battery and alternator might test 'good' under simple load, the issue could be more nuanced.

Here's a breakdown of potential causes and steps:

  1. Parasitic Draw Test: This is crucial. A component might be staying active when the vehicle is off, slowly draining the battery. This often requires a multimeter and patience, checking fuses one by one after the vehicle has 'gone to sleep' (usually 15-30 minutes after turning off).
  2. Alternator Diode Failure: Even if an alternator 'passes' a basic test, a failing diode can cause a slight draw or inefficient charging, especially under specific conditions. This might not always throw a hard code but can lead to battery issues.
  3. Battery Age: While it tested okay, an original battery from 2018 is nearing the end of its typical lifespan (3-5 years). A weak battery can struggle to hold a charge, especially if there's any minor draw.
  4. Body Control Module (BCM) Issues: The BCM controls many electrical functions. A fault here could cause components to remain active or mismanage the charging system. This might trigger codes like P0562 (System Voltage Low) or P0560 (System Voltage Malfunction) if the BCM detects an issue.
  5. Wiring or Ground Issues: Corroded or loose ground connections can lead to charging system inefficiencies or unexpected electrical behavior.

When to See a Shop: If you're not comfortable performing a parasitic draw test or if the issue persists after checking basic connections, it's best to take your Sierra to a qualified mechanic or GMC dealership. They have specialized diagnostic tools to pinpoint intermittent electrical faults and can check for specific trouble codes related to the charging system or BCM that might not trigger a check engine light.

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