Lost Communication With EV Traction Battery Module B
The U0221 code means the vehicle's onboard diagnostic system has detected: Lost Communication With EV Traction Battery Module B. This is a critical severity code.
- Keep driving?
- No -- stop driving
- DIY difficulty
- hard
- Estimated cost
- $1,500 - $8,000 (parts and labor)
Network codes mean modules are not communicating. You need a scanner that reads all systems to find the problem.
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Common Symptoms
- Battery system fault warning
- Reduced or no range available
- Vehicle shuts down unexpectedly
- Traction battery warning light
- Cannot charge the vehicle
Probable Causes (Ranked by Likelihood)
- Failed traction battery module B controller Very High
- High-voltage bus fault in module B High
- Cell imbalance in battery module B Moderate
- CAN bus communication disruption Low
Step-by-Step Diagnostic Procedure
-
Scan traction battery module B for fault codes
-
Check high-voltage connections to module B
-
Test individual cell voltages in module B
-
Verify CAN bus wiring to battery module B
Frequently Asked Questions
Can I drive with U0221?
No. Critical battery communication failure. The vehicle may shut down while driving.
What causes U0221?
Typically a failed battery module B controller or high-voltage connection issue.
How is U0221 different from U0220?
U0220 is module A and U0221 is module B. Large packs have multiple modules.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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