Codes E1/E2/E3/E4/E5/E6/E8 all instruct 'Contact the after-sales service' (no user-serviceable action defined). E7 (motor temperature) instructs to stop use and charge fully until the warning clears. E9 (battery temperature) instructs to stop use and let the unit return to room temperature until the code disappears.
Fuente oficial: https://cdn.decathlon-share.com/product-user-guide/9d5c0508ab20a/manuel-utilisateur-sd500-25kmh.pdf (tier A). Traducción/paráfrasis fiel del manual oficial; no se ha añadido ningún procedimiento no documentado.