correct, thats the knock sensor. It will throw a CEL but I can't tell you if it will hurt anything or not, so far so good for mine because it has been broken for over a year. It is useful to a certain extent I suppose. The knock sensor sends a signal to the ecu and when a high enough "knock" is detected, the ecu will pull some timing. I broke the one in my civic when i installed a supercharger, been running for over a year now with no problems. If you chip your ecu and use uberdata you can disable it to get rid of the check engine light, or you can shell out the $$$ and buy a new one.