BMS family
BMS_a151_SW_external_isolation
Vehicle may not restart
What does the BMS_a151_SW_external_isolation alert mean?
The battery management system (BMS) detects that high voltage (HV) isolation is too low while pack contactors are closed.
What you'll see in your Tesla
- Vehicle may not restart
- Service is required
What triggers it
The BMS has detects that HV isolation is below the warning threshold while contactors are closed.
When it clears
The BMS has detects that HV isolation is within the acceptable threshold while contactors are closed.
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.