Power Limited — High Voltage Isolation Fault (Vehicle May Not Restart)
The TESLA-BMS_A027 (Tesla BMS (Battery Management System)) EV fault code means: Power Limited — High Voltage Isolation Fault (Vehicle May Not Restart). This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- expert
- Estimated cost
- Diagnosed and quoted by Tesla service; isolation faults can range from a damaged component or moisture intrusion 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: "Power limited - OK to drive — Vehicle may not restart after this drive"
- Reduced power while driving
- Vehicle may be unable to restart after the current drive
- May appear alongside other high-voltage or BMS alerts
Probable Causes (Ranked by Likelihood)
- The high-voltage system's electrical isolation from the chassis has dropped below the acceptable threshold across multiple drive sessions (Tesla's official description); the vehicle limits performance to protect the system Likely
Step-by-Step Diagnostic Procedure
Take this alert seriously: the high-voltage system is designed to stay electrically isolated from the vehicle chassis for safety, and this alert means that isolation has been repeatedly compromised.
Note the contradiction in Tesla's own text: the alert title says "OK to drive," but the official what-to-do guidance says to schedule service immediately and NOT to drive the vehicle further until it has been inspected by Tesla Service. Follow the stronger guidance — stop driving and get it inspected.
The vehicle may be unable to restart if the condition persists, so don't park it somewhere you can't recover it from.
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_a027 mean on a Tesla?
Tesla's official meaning: the high-voltage system's electrical isolation from the chassis has dropped below the acceptable threshold across multiple drive sessions. The vehicle limits performance to protect the system, and it may be unable to restart if the condition persists.
The alert says OK to drive but service says don't — which is it?
Tesla's alert title reads "Power limited - OK to drive," but the official what-to-do text says to schedule service immediately and not to drive the vehicle further until Tesla Service has inspected it. Follow the stronger instruction: stop driving and schedule service immediately. Repeated isolation loss is an electrical safety issue, not just a performance one.
Can my Tesla really fail to restart with BMS_a027?
Yes — Tesla's official text says the vehicle may be unable to restart if the condition persists. Park it somewhere accessible and arrange service promptly rather than risking a stranded vehicle.
Sources
This page is built from documented references. Verify against your own service info before repair work.