You wouldn't get a signal!
The O2 sensor needs to reach 600 degrees farenheit to put the engine in closed loop, then the coolant temprature sensor puts the computer in a total closed loop state when it reaches it's specified temp: 195, 200, 205.
Refinish King
I've been reading thru the archives wrt O2 sensors, such as
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> On a 3-wire ZrO2 sensor, does the sensor shell or body, threaded to
> the exhaust downpipe or similar, act as the ground?
>
> i.e., two of the wires are for the integrated heater circuit, with one
> supplying power, and the other the ground (for the heater circuit) >
> The 3rd wire is the signal wire, ~ 0V - 1V (0.2V - 0.8V) input to the
> ECU. But doesn't that wire need a ground (in several wiring diagrams
> I've looked at, the ground symbol is never shown for it at the
> downpipe area). A post or two do stress cleaning the O2 sensor
> mounting point. But the signal voltage is so low, wouldn't it need a
> cleaner ground than an exhaust pipe, which would ultimately ground
> it's way thru gaskets, to the head or engine block, then onto the
> battery negative terminal?
>
> I might do this to learn some time - what would happen if the O2
> sensor was pulled from the exhaust pipe, left connected to the ECU,
> and just placed in open air? Inside O2 levels vs outside O2 levels
> would be the same - no differential for voltage - but it's no longer
> grounded(?)? What would the signal wire output or ECU input voltage > read?