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2018 Cadillac CT6 Battery Drain Issue - Dead Battery Overnight

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Mike T. · rep 0 · May 22, 4:00 AM · 1 replies · solved · Question

Vehicle: 2018 Cadillac CT6 Premium Luxury

Hi all,

I'm having a persistent problem with my 2018 Cadillac CT6 Premium Luxury. For the past few weeks, if I leave it parked for more than 12-18 hours, the battery is completely dead. I've had to jump-start it multiple times, and it's getting really frustrating. I had the battery tested, and it's supposedly good, and the alternator is charging fine when the car is running.

It feels like there's something draining the battery while the car is off. I don't have any aftermarket accessories installed, and I always make sure all lights are off and doors are closed. Has anyone experienced a parasitic draw on their CT6 or similar Cadillac models? What should I be looking for? Any advice would be greatly appreciated.

Thanks!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:00 AM

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ClearTheCode admin answer:

A parasitic battery drain on a 2018 Cadillac CT6 can be notoriously difficult to diagnose, as modern vehicles have many modules that remain active for a period after the car is shut off. When the battery dies overnight, it indicates a significant draw that isn't shutting down properly.

Common Causes of Parasitic Draw:

  • Faulty Modules: A module (e.g., infotainment, OnStar, BCM, door module) failing to enter 'sleep mode' can continuously draw power.
  • Stuck Relays: A relay that remains energized when it shouldn't be.
  • Interior/Trunk Lights: Even a small light left on due to a faulty switch or sensor.
  • Key Fob Proximity: If the key fob is left too close to the vehicle, some systems might remain active, anticipating use.
  • Aftermarket Accessories: Though you mentioned none, even a poorly installed dash cam or radar detector can be a culprit.

Troubleshooting Steps (DIY with caution):

  1. Multimeter Test: Disconnect the negative battery terminal. Connect a multimeter in series between the negative battery post and the negative battery cable (set to amperage, typically 10A or 20A range). Wait at least 30-60 minutes for all modules to 'sleep.' A normal draw should be under 50mA (0.05A). If it's significantly higher, you have a draw.
  2. Fuse Pulling: While monitoring the multimeter, systematically pull one fuse at a time from the fuse boxes (under the hood, trunk, and passenger compartment). When the amperage drops significantly, you've identified the circuit with the draw. This narrows down the faulty component.
  3. Check for Visible Lights: Double-check glove box, trunk, and vanity mirror lights. Ensure they turn off when closed.
  4. Key Fob Distance: Try leaving your key fob far away from the vehicle overnight to see if it makes a difference.

When to See a Shop: Diagnosing parasitic draws can be time-consuming and requires patience. If you're uncomfortable with electrical testing or can't pinpoint the source, a professional shop is recommended. They have specialized diagnostic tools that can monitor module activity and current draw more precisely. They can also check for specific diagnostic trouble codes (DTCs) related to module communication or low voltage (e.g., B-codes or U-codes) which might indicate a module that isn't shutting down correctly.

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