BMS_a066
Tesla Electric Vehicle
Severity: ModerateWhat Does This Error Mean?
Tesla BMS_a066 is a battery management alert that reads 'Maximum charging power reduced'.
It is not a hard fault.
The car still drives and still charges — but at a lower peak rate than the connector and the battery would normally allow.
Causes range from a chilly battery on a winter morning to long-term wear that the BMS is now respecting.
The alert often clears on its own once conditions improve.
Affected Models
- Tesla Model 3
- Tesla Model Y
- Tesla Model S (refreshed and pre-refresh)
- Tesla Model X (refreshed and pre-refresh)
Common Causes
- Cold battery — peak rate restored after preconditioning
- Hot battery after a long Supercharger session or aggressive driving
- High state of charge — Tesla deliberately throttles past about 80%
- Charge port or charge cable temperature flag
- Long-term cell imbalance the BMS is compensating for
- Earlier high-voltage fault that left a derate flag
How to Fix It
-
Precondition the battery before charging.
Set the destination to a Supercharger in the navigation, even if you are already there.
The car warms the battery to charging temperature on the drive in.
For home charging in winter, schedule a departure time and the car preconditions on a charger. -
Let the battery cool after a long drive.
If you arrived at a Supercharger after a long highway run, the battery is hot.
BMS_a066 may show for the first 5-10 minutes.
Keep charging — peak rate generally returns once temperatures normalise. -
Charge to no higher than 80% for daily use.
Charging above 80% is naturally slower on every Tesla — that is by design and not a fault.
Set the daily charge limit at 80% in the app.
Use higher only for road trips. -
Try a different charger.
If BMS_a066 only appears at one specific Supercharger or one home connector, the issue may be on that side — a hot stall, a worn cable, or a connector that throttles itself.
Try a different stall or a different home cable to isolate. -
Drive a few full cycles.
BMS calibration improves with normal cycling.
Drive the battery from above 80% down to below 20% a few times over a week, charging fully back at home.
Mild derate flags often clear during this learning. -
Schedule service if the alert persists.
If BMS_a066 stays on for weeks regardless of temperature and state of charge, request service in the app.
Tesla can pull battery diagnostic logs and decide whether the pack itself or a sensor is the cause.
Many derate codes resolve with a software refresh — others are a sign of cell wear approaching warranty thresholds.
Frequently Asked Questions
Will BMS_a066 affect range?
Not directly.
Range depends on usable battery capacity, not peak charging power.
You can still drive the same distance — it just takes longer to fill the battery back up at the next charging stop.
Is this covered by the battery warranty?
If the alert points to underlying capacity loss below the warranty threshold (70% of original on Model 3 and Y over 8 years/120,000 miles, varying by model), Tesla service handles it.
BMS_a066 alone is not a guaranteed warranty event — diagnostic logs decide.