Diagnostics, logging and fault codes
Reading what the pack has been through.
You'll learn
- Explain diagnostics, logging and fault codes at engineering level
- Read the numbers that define the behaviour
- Apply the idea to a real pack
Overview
Every modern BMS keeps a black box: extreme temperatures, peak currents, cell deltas and fault history. That log is the most honest description of a used EV.
In depth
| Signal | Healthy | Investigate |
|---|---|---|
| Cell voltage delta at rest | < 20 mV | > 60 mV |
| Max cell temperature spread | < 5 °C | > 10 °C |
| Isolation resistance | > 1 MΩ | < 500 kΩ |
| Capacity vs new | > 90% at 3 years | < 85% at 3 years |
Activity
Match the symptom to the cause
Rapidly dropping range in the last 10%
→Charging power much lower than rated
→Sudden isolation fault after rain
→Key takeaways
Remember this
- The BMS log is the pack's real history.
- Cell delta and temperature spread are early warnings.
- Health reports beat dashboard range estimates.
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