US Patent 7562558 Knock sensor diagnostic system and method

A knock sensor diagnostic system may include a knock sensor. A bias circuit applies a bias voltage to the knock sensor. An input circuit receives an input signal based on the bias voltage. A control module indicates a short circuit associated with the knock sensor based on the input signal. A knock sensor diagnostic system may also or alternatively include a signal generator that generates and applies a test signal with a predetermined frequency to the knock sensor. Another input circuit receives another input signal that is based on the test signal. A control module indicates an open circuit associated with the knock sensor based on the other input signal.