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2018 CT6 Battery Draining Overnight - Parasitic Draw Mystery

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Mike T. · rep 0 · May 22, 3:59 AM · 1 replies · solved · Question

Vehicle: 2018 Cadillac CT6 Premium Luxury

Hi all,

I'm at my wit's end with my 2018 Cadillac CT6 Premium Luxury. For the past few weeks, the battery keeps dying overnight. I've had it jump-started multiple times, and even replaced the battery with a brand new one, but the problem persists. If I don't drive it for 12-24 hours, it's completely dead.

There are no warning lights on the dash, and everything seems to work fine when the car is running. I've checked to make sure all lights are off, doors are closed, and nothing is plugged into the accessory ports. Could this be a parasitic draw from some electrical component? What's the best way to track something like this down?

It's incredibly inconvenient, and I'm worried about damaging the new battery. Any ideas on what modules or systems are common culprits for this type of issue in a CT6?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:59 AM

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ClearTheCode admin answer:

A recurring battery drain, even after replacement, strongly indicates a parasitic draw. This means an electrical component or module is staying active and consuming power when the vehicle is supposed to be off. Tracking these down requires systematic diagnosis.

  1. Confirm the Draw: First, a technician will use an ammeter to measure the current draw from the battery with the vehicle fully 'asleep' (all doors closed, key fob away, wait 15-30 minutes for modules to power down). A healthy draw is typically under 50 milliamps (0.05 amps).
  2. Fuse Pull Method: Once a significant draw is confirmed, the technician will systematically pull fuses one by one while monitoring the ammeter. When the draw drops significantly after pulling a specific fuse, it isolates the circuit responsible for the draw. This points to the module or components on that circuit.
  3. Common Culprits: In modern Cadillacs like your 2018 CT6, common sources of parasitic draws include:
    • Infotainment/CUE Module: Can sometimes fail to power down correctly.
    • OnStar Module: If it's malfunctioning or constantly trying to communicate.
    • Body Control Module (BCM): A faulty BCM can keep various systems awake.
    • Door Lock Actuators: A faulty actuator can keep the BCM awake, thinking a door is ajar.
    • Alternator Diode Failure: A failing diode in the alternator can create a short, allowing current to flow from the battery when the engine is off.
    • Aftermarket Accessories: Any non-factory installed electronics can be a source.
  4. Diagnostic Trouble Codes (DTCs): While a parasitic draw might not always trigger a Check Engine Light, a full scan of all vehicle modules (not just the engine) can sometimes reveal 'U' codes (network communication issues) or 'B' codes (body electrical issues) that point to a module that isn't shutting down properly.

When to See a Shop:

Diagnosing a parasitic draw can be complex and time-consuming, requiring specialized tools and knowledge. It's highly recommended to take your CT6 to a Cadillac dealership or an experienced automotive electrical specialist. They have the necessary diagnostic equipment and wiring diagrams to accurately pinpoint the source of the draw without damaging sensitive electronic components.

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