SW900 LCD · Current
21 SW900 LCD error code 21
Current abnormality
Widely published – may differ by model/firmware
Note
Common error table of generic Chinese LCD displays (JN-type controllers). The paired controller defines the actual meaning.
Possible causes
General, component-based causes – not a manufacturer-specific statement.
- Over-current (short circuit, stalled motor)
- Faulty current sensor in the controller
- Phase short in the cable
Safe test steps
- Free wheel rotation unpowered; phase cable damage.
- Phase resistance symmetry without the controller.
Workshop reference values
- No general documented measurement value – manufacturer service documentation required.
Repair approach
- Remove the short; if it repeats, check/replace the controller.
Tools needed
- Digital multimeter (CAT III, fused inputs)
- Basic hand tools, insulated screwdrivers
Safety
- Do not repeat the test if the controller heats up or smells burnt.
This information does not replace manufacturer service documentation. Work on batteries and high-voltage parts only with the appropriate expertise.