Your numbers don't make any sense. O2 sensor voltages can't be 8. something. You need to give me numbers with units after; such as 0.727v or 20ma. You need to verify your readings with a standard.
If you wish to look at the EHA control it is done at the eHA and will be in ma and key on engine off should equal 20ma. See if this happens. O2 sensor voltage should never be anything but 0 to 1v. If you read the lead to the computer it should read .45v when disconnected from the sensor.
If you have O2 sensor voltage above 1v then the heater circuit is bleeding voltage through. It runs at battery voltage so in theory anything up to that could be transfered.
Bosch Master, ASE Master, L1
33 years MB technician