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Excessive Phantom Drain & 12V Battery Warning on 2021 Model 3 Performance

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Mike T. · rep 0 · May 25, 4:02 AM · 1 replies · solved · Question

Vehicle: 2021 Tesla Model 3 Performance

Hi everyone, I'm experiencing some concerning issues with my 2021 Tesla Model 3 Performance. Over the past few weeks, I've noticed a significant 'phantom drain' when the car is parked overnight. I can lose anywhere from 5-10% of my main battery charge, even with Sentry Mode off, cabin overheat protection off, and no third-party apps connected.

To top it off, yesterday I got a '12V Battery requires service' warning on my screen. I know the 12V battery is critical even in an EV. Could these two issues be related? Is the excessive drain putting a strain on the 12V system, or is a failing 12V battery causing other systems to draw more power?

I'm trying to figure out if this is something I can troubleshoot myself or if it's an immediate service center visit. Any thoughts on common culprits for high phantom drain or what to check regarding the 12V battery?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 4:02 AM

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ClearTheCode admin answer:

These two issues – excessive phantom drain and a 12V battery warning – are very likely related and point to a potential problem within your 2021 Model 3 Performance's electrical system. The 12V battery is crucial for powering the car's auxiliary systems, including the contactors that connect the main high-voltage battery. If it's weak, it can cause various electrical anomalies.

Here's a breakdown:

  1. Failing 12V Battery: The '12V Battery requires service' warning is a direct indicator. In Teslas, the 12V battery is a conventional lead-acid (or increasingly, a lithium-ion in newer models) battery that powers all the low-voltage electronics. A failing 12V battery can cause the main high-voltage battery to work harder to keep it charged, leading to increased phantom drain. It can also cause erratic behavior in various electrical components.
  2. Parasitic Drain Sources: Even with Sentry Mode and Cabin Overheat Protection off, other factors can cause phantom drain:
    • Third-Party Apps: Any third-party apps that constantly poll your car's data can keep systems awake.
    • Frequent App Checks: Regularly checking your car's status via the Tesla app can wake up the vehicle and consume power.
    • Summon Standby: If Summon Standby is enabled, the car keeps certain systems active.
    • Software Glitch: A software bug could be preventing the car from entering a deep sleep state.
  3. HV Battery Contactor Cycling: If the 12V battery is weak, the main battery contactors (which are 12V controlled) might cycle more frequently or struggle to engage, leading to inefficient power management and increased drain.
  4. Internal Diagnostic Codes: Tesla's internal diagnostics will likely show codes related to the 12V system, such as CC_w026 (12V battery fault) or BMS_f001 (12V system under-voltage).

When to see a shop:

Given the explicit '12V Battery requires service' warning, you should schedule a service appointment with Tesla immediately. A failing 12V battery can lead to your car being completely bricked (unable to start or respond) without warning. While the phantom drain might be a symptom, the 12V battery warning is a critical alert that needs prompt attention. Tesla service can test the 12V battery, replace it if necessary, and diagnose any other parasitic drains or electrical system faults.

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