How to EFIE a 2005 prius?

all

I have built a nice big 14-cell HHO unit with PWM.

For this to be useful i have also gotten myself a digital EFIE to push the A-F ratio sensor (narrow band placed before cat) voltage value a bit up to simulate rich mixture. This should make the EFI leaner.
But... in every document i find about the Pinout on the ECM ECU, this A-F ratio sensor is connected to one pin A1A+ with constant 3.3V and another A1A- that seem to be constant 2.8V or so. On other cars i have never seem similar arragement. Normal cars use the sensor to produce a voltage that is used as is, but this is new and strange for me.

I have tried to connect the EFIE to manipulate voltage only by 0.03V in both directions, but i get an error saying something like "oxygen sensor pumping current to low" on the A-F ratio sensor after a few minutes of driving, at the same time as the 2.8 Volts drops to 0V.
The unit i have can also produce current adding if i want but i havnt tried that because this is meant for wide band sensors.
Does anyone have a clue how this sensor is working together with the ECM ?

Best regards
Jonas Hansson

2005 European executive Prius.