Mercedes W210 Knock Sensor Open Circuit Fault Code: Diagnosis and Solutions

I took my Mercedes W210 to a mechanic, who used an Autoland Scientech D91 scanner and detected a knock sensor open circuit fault code. The issue is intermittent — after clearing the stored code, the warning disappears temporarily but returns shortly thereafter. Although no active fault code is currently being triggered, the stored knock sensor open circuit code persists (the exact code number is unclear at this time). Additionally, during diagnostics, the O2 sensor control reading showed negative values between -1% and -2%. I should note that my vehicle has only one oxygen sensor located at the exhaust manifold, not at the catalytic converter. I'm looking for help identifying the most likely cause of this issue. Can anyone confirm whether a knock sensor open circuit typically indicates a wiring problem, sensor failure, or mechanical damage? Also, where can I find a comprehensive list of OBD2 fault codes with detailed explanations for Mercedes W210 models? Any reliable source or official documentation would be greatly appreciated. Thanks in advance for your insights.