69. The owner of a bus or minibus shall maintain the following systems and equipment in proper working order: the loading ramp, the power lift platform, the emergency exit door, the locking and unlocking devices for doors, the securement devices for wheelchairs, the safety belts, the rims, the tires, the braking system, exhaust, heating, ventilation and defrost systems, the buzzers, the windshield wipers and the chemical extinguisher.