What is a Knock Sensor and where is it located on a 2001 Altima GXE?

Answer 1

The knock sensor is a Non Check Engine Light item (shows a code) won't light the MIL mallfunction indicator lamp. Ping from low grade fuel noise is high frequency noise picked up by the microphone that's what a knock sensor is. That signals the engine control to retard the engine spark timing. The location is difficult to get to. Wait till the next oil change because you have to remove the oil filter's adapter on the back side of the engine to get enough room to replace the sensor located in the engine block middle near the cyl head under the intake manifold.