Knock Sensors - Code 25
 

I got a diagnostic code 25 for 1993 300E 2.8 which indicates knock sensor problem. Is anybody familiar with this one? Could it be a loose wire that can just be plugged back in? If the sensor or sensors are bad (I don't know how many exist in this car) where are they? Is it a DIY thing or do I need a shop? Is there a DIY steps somewhere in this forum for this problem? Answers to these questions will be greatly appreciated.