Vehicle May Not Restart — HV Isolation Fault (Do Not Charge)
The TESLA-BMS_A151 (Tesla BMS (Battery Management System)) EV fault code means: Vehicle May Not Restart — HV Isolation Fault (Do Not Charge). This is a serious severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- expert
- Estimated cost
- Diagnosed and quoted by Tesla service; isolation faults range from moisture/component issues to major pack work. Battery-related repairs may be covered by the battery and drive unit warranty — check your coverage.
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Common Symptoms
- Alert on the touchscreen: "Vehicle may not restart — Service is required"
- Vehicle may be unable to charge, drive, or support other vehicle systems
- Detected while driving or charging
- May appear alongside other high-voltage or BMS alerts
Probable Causes (Ranked by Likelihood)
- Reduced electrical isolation detected in the high-voltage system while driving or charging (Tesla's official description); the vehicle limits functions when isolation falls below acceptable levels Likely
- Firmware-level alert name (BMS_a151_SW_external_isolation, per the firmware alert dictionary) indicates isolation measured too low on the EXTERNAL side (outside the pack) while the battery contactors are closed Possible
Step-by-Step Diagnostic Procedure
This is a high-voltage electrical-safety alert detected while driving or charging, and Tesla's guidance for it is stricter than its sibling BMS_a035: do NOT attempt to charge the vehicle.
Per Tesla's official text, the vehicle may be unable to charge, drive, or support other systems, and you should schedule service if the alert persists.
Tesla's safety escalation applies: if you notice any unusual smells, sounds, or visible damage near the battery area, stop using the vehicle immediately and contact Roadside Assistance.
High-voltage isolation diagnosis is Tesla-service-only work — never attempt to inspect or repair the high-voltage system yourself.
Frequently Asked Questions
What does BMS_a151 mean on a Tesla?
Tesla's official meaning: the vehicle detected reduced electrical isolation in the high-voltage system while driving or charging. The high-voltage system is electrically isolated from the vehicle frame for safety; when isolation falls below acceptable levels, the vehicle limits certain functions and may be unable to charge, drive, or support other systems.
Can I charge my Tesla with BMS_a151?
No — Tesla's official guidance says do not attempt to charge the vehicle. Schedule service, and if you notice unusual smells, sounds, or visible damage near the battery area, stop using the vehicle immediately and contact Roadside Assistance.
What's the difference between BMS_a151 and BMS_a035?
Both report reduced high-voltage isolation detected while driving or charging. BMS_a151 carries the stricter guidance — do not charge, and involve Roadside Assistance if anything near the battery seems unusual — which suggests the detected condition is treated more seriously.
Sources
This page is built from documented references. Verify against your own service info before repair work.
- Tesla Model 3 Owner's Manual — Troubleshooting Alerts (official Tesla alert text for BMS_a151)
- Tesla Model Y Owner's Manual — Troubleshooting Alerts (confirms BMS_a151 is documented across models)
- Tesla firmware alert reference (core-hacked/tesla-alerts-dictionary): bms_a151
- Tessie Tesla alert statistics