GoKawiilApple's troubleshooting steps for AirPods with one dead earbud
When only one AirPod produces sound, the likely cause is a charging problem. Owners are advised to clean the case's charging port and contacts, fully charge the case, then check both AirPods' battery status via the iPhone popup or Batteries widget before testing the faulty earbud alone. If cleaning and recharging don't fix it, a factory reset through iPhone Bluetooth settings is the next step, with slightly different reset button sequences for older versus newer AirPods models.