Aventon Pace 500.3/Solon/Sinch.2 — Error Code E21
Reviewed by certified eBike technicians · Last updated July 15, 2026
Quick Answer
E21 on Aventon = Speed sensor signal lost — wheel speed not detected
Severity: Check soon — speed reading lost · Limited riding OK, diagnose soon
Error E21 on your Aventon indicates: Speed sensor signal lost — wheel speed not detected.
Check soon — speed reading lost — Speed sensor signal lost — wheel speed not detected
Symptoms
- E21 on display; speed shows 0 even when riding; motor may default to walk mode only; PAS may not engage properly
Common Causes
- Speed sensor magnet fell off rear wheel spoke
- Speed sensor on chainstay moved out of range
- Sensor wire damaged from road debris
- Magnet too far from sensor (>10mm gap)
- Sensor connector loose at controller
Fix Steps
Step 1: 1. Check the speed sensor magnet on the rear wheel spoke — it should be present and secure
Step 2: 2. If magnet is missing: replace with any spoke magnet (5mm diameter standard)
Step 3: 3. Check the sensor pickup on the chainstay — it should be within 5-8mm of the magnet
Step 4: 4. Clean both the magnet and sensor face
Step 5: 5. Spin the rear wheel by hand and verify speed reading on display
Step 6: 6. If still showing 0: check the sensor wire for cuts from road debris or chain slap
Step 7: 7. Replacement speed sensor kit: ~$15-20 online
Related Error Codes
Error E01
Motor hall sensor fault — controller cannot read motor position
Error E04Battery communication error — BMS and controller not communicating
Error E07Controller overtemperature — motor controller exceeded 85°C internal limit
Error E10Brake sensor engaged — brake cutoff switch stuck or misaligned
Always disconnect the battery before inspecting wiring.