Customer Complaint
Vehicle went into limp mode with “Reduced Power” and “Vehicle may shut down” alerts. No recent collision.
System Theory
The pyro-fuse in the battery penthouse permanently disconnects the pack if overcurrent or crash is detected. BMS_a066 indicates pyro-fuse or contactor failure.
Diagnostic Testing
- Service Mode showed BMS_a066 – “Pyro fuse status: FAILED”
- Isolation test failed at 0.3 MΩ
- Pyro-fuse continuity: open
Root Cause
Failed high-voltage pyro-fuse inside battery pack penthouse (common on 2021–2023 models).
Repair Procedure
- Full HV battery pack replacement (remanufactured unit)
- Commissioned via Toolbox 3
- Cleared alerts – full performance restored
Parts Used
| Description | Part Number | Qty | Price |
|---|---|---|---|
| Battery Pack (Reman) | 1108673-00-F | 1 | $13,500.00 |
| Labor | — | 6.2 hrs | $930.00 |
Key Lessons
- BMS_a066 = pyro-fuse blown → full pack replacement
- Tesla does not sell pyro-fuse separately
- Always check for minor rear impacts
- Reman packs save thousands vs. new
Submitted by: Sarah Kim – Tesla Certified HV Technician, Seattle, WA