Oxygen sensor not okay

0.44 is the default voltage the ECU goes to if it doesn't see the voltage.
In normal conditions the voltage should vary between 0.1 and 0.9v.

O2 sensor will sit static at 0.44v at ecu if the system is running open loop.  This means all values are defaulted, o2 levels and fueling map then runs rich just as if it was in auto choke during startup which is also open loop.
there are other factors e.g. if ur coolant sensor was stuck saying cold the car would stay open loop and never swap over to read o2 sensor values.  You see what i mean.  Check your other readings and only when the car is up to temp and ready will it swap over to closed loop values.   Another reason is that it drives a heater in the o2 sensor to Heat it up so it can work correctly.  If this relay or drivers doesn't work again it wont go closed loop so check heater values for voltage on startup of car and periodically after.  Ive asked seperately for a list of things that impact open loop decision so i hope it helps if answered.  All mems ecus perform in similar mannor for open closed loop so doesnt really matter if mems1.6 or mems3.  Only real difference is if it uses a relay pack or drivers direct from ecu or bcu.   Tnx.

I have exactly the same problem, replaced with, new original OE sensor from Rimmers, same result.
Now I have checked the wiring from the lambda sensor plug to the ecu and there is continuity.
Are the heater sensor wires the white wires? What readings should I expect?

The MEMS 1.9 ecm, does not control the heater circuit directly, it operates a relay in the Engine Management Relay Module, which is the black unit attached to the ECM bracket, behind the ECM. The heater circuit of the lambda or sensor heated oxygen (HO2S) is supplied voltage from the relay via a blue with red trace wire to the sensor plug and earthed via a black wire to a body Earth point.
The relay is switched by earthing the relay coil via a black with green trace. The relay live feed is from the engine control relay also situated in Engine Management Relay Module on a brown wire fed from fuse 2 in the under bonnet fuse box.
Check for voltage on the blue and red wire, with a multi meter, should be 12v.
I was getting the same static readings 0.44 v, sensor not ok, tried three different sensors.
The other two wires on the sensor are the signal wires from the sensor to the ECM, light green and grey (slate) and grey (slate), although I think that you would require the use of an oscilloscope to read the output on these.
Even swapped ECM s but no difference.
I gave up in the end and converted my F to MEMS 3, as I had already fitted 135 cams, alloy manifold and blue injectors.
I hope this helps.
If someone works out what the actual problem is I would be interested to know !