Duty-cycles of 2.6 or 3.4 don't mean anything. I would interpret those readings as zero on pin three.
You need a reference. I still don't remember what car we are talking about but you should have 70% duty cycle on most vehicles with the key on and engine off. Duty cycle readings of a fixed amount that is a multiple of 10 are codes and an active reading gives a function of control (relative mixture).
All cars should have a reading of 50% with the O2 sensor disconnected. Get your readings gauged to one of these constants before deciding what you have in active mode.
Bosch Master, ASE Master, L1
33 years MB technician