Knock sensors are never 'stuck'. It's basically a microphone that's tuned to listen to engine knock and convert them to electrical pulses. If the ECU stops receiving these pulses due to a broken sensor, noise instead of pulses are heard, disconnected/open circuit or short circuit, a DTC is raised and the engine, 'deaf' at detecting engine knock, won't be able to correct the timing, will maintain a rich A/F mixture, and finally goes into limp-mode (reduced output power and/or speed) to protect itself.