Internal Battery Pack Monitor Communication Loss
The Battery Management System dropped its data connection with an internal cell-monitoring circuit card inside the HV battery casing. Without real-time cell temperature and voltage data, the car caps charging and range to protect the pack from thermal runaway.
Do not charge with active overvoltage warning.
Estimated Cost
$1,650
Repair Time
Dealer visit required
Difficulty
Dealer Only
Can I Fix This Myself?
Professional Service Recommended
This repair involves high-voltage components or specialized equipment.
What professionals will use:
Use the diagnostic wizard below to gather information for your mechanic, then find a local EV specialist using the ad below.
Step-by-Step Fix Instructions
- 1
Apply any pending OTA firmware updates via the main screen.
- 2
Run detailed validation on low-voltage communication gateway plugs with enterprise diagnostic scanner.
- 3
Schedule service center transport — requires specialized HV safety facilities.
- 4
Drop and slide out the structural battery pack from underneath the chassis.
- 5
Unseal the outer battery shell and navigate past interior cell modules.
- 6
Locate and replace the uncommunicative internal monitoring board and its flex-ribbon cable.
Check Your Warranty Before Paying
Federal law requires EV battery warranty coverage for 8 years / 100,000 miles minimum. Many manufacturers offer 10-year coverage. An authorized dealership can confirm coverage for your VIN at no charge.
Step-by-Step Diagnostic Wizard
Answer each question to narrow down the root cause of your BMS_u029 fault.
Check Vehicle Driveability
Step 1 of ~5
Attempt to enter Drive mode. Note if the car is in Limp Mode (reduced acceleration), displaying a red battery warning, or completely unable to drive.
Is the vehicle driveable (enters Drive mode) even if showing warnings?
Need hands-on help?
Find a verified EV mechanic or dealership near you.