iPod 4th Generation (Latest possible OS) stuck in 'Headphone' Mode

My old iPod 4th Generation iPod is stuck in 'Headphone' mode. I've blown into the headphone jack, pulled in and pulled out the headphones while the iPod was On/Off. I also restored the iPod, backing it up afterwards. None of the things I've done have helped and the iPod is still stuck in 'Headphone' mode. Audio works fine when headphones are actually plugged in, and so does sound testing in Settings.