BMS family
BMS_a123_SW_Internal_Isolation
Unable to charge
What does the BMS_a123_SW_Internal_Isolation alert mean?
The battery management system (BMS) detects that there is low high voltage isolation when pack contactors are opened.
What you'll see in your Tesla
- Unable to charge
- Service is required
What triggers it
The BMS detects that isolation dropped below the minimum threshold when pack contactors were open.
When it clears
The BMS detects that isolation is above the minimum threshold when pack contactors are open.
Potential impact
Inability to charge, drive, or support the low voltage (LV) system
Affected models
Model 3 2017-2023
Model 3 2024+
Model S 2021+
Model X 2021+
Model Y
Model Y 2025+
Track your Tesla's alerts automatically
Alerts like this reach MyTeslaMate through your car's Tesla telemetry API. MyTeslaMate logs every alert your Tesla reports and turns it into readable history and real-time notifications — hosted TeslaMate with no server to run.