Car: 1990 300SEL California Version 103 Engine

Just bought a new/used 1990 300SEL. A beautiful car with 83,000 miles. It was idling kind of rough, but no CEL; or so I thought. I noticed that the CEL was not lit in key position 2, so I replaced the bulb and sure enough, with the engine running the CEL was on and signaling a fault. Not what I wanted to see especially when I had a Mercedes mechanic do a PPI for me.

I did some archive research, checked the onboard LED and it gave me 17 flashes. By Arthur Dalton’s CS 1000 Fault code scanner document, I read 17 flashes as “O2 Sensor Shorted to Positive or Negative”.

I have three questions:
I'm not sure I'm reading the right chart. Can someone please confirm my conclusion?
I assume I need a new O2 sensor, but what exactly does this “Short” mean?
I noticed another O2 fault code called “Signal Illogical”. How do they differ?

Thanks, any help would be greatly appreciated.

Outofspec