Wideband oxygen sensors actually make use of a narrowband sensor, but with some additions. Specifically there is a control input on the sensor that allows the stoich point to the shifted rich or lean, based on how much current is injected into that control input. This means that with a specific amount of control, the sensor can behave like a 13.5:1 stoich sensor for example. So the output would be 0.45 Volts at 13.5 AFR. Or it can be made to be leaner than 14.7:1 AFR. The changeable range is about -50% to +50% for a common Bosch wideband O2 sensor.
Now, a wideband sensor HAS the ability to detect and measure air-fuel ratios other than 14.7, but it requires a varying control to do so. This is the job of a wideband controller. It dynamically and VERY rapidly adjusts the amount of current to the sensor control input to get an output of 0.45 Volts. At that point, the controller knows what AFR ratio is stoichiometric for the amount of current injected into the control input, and can calculate the air-to-fuel ratio from that. This is typically puts out as a varying analog voltage for a gauge or ECU.
And there it is... without a controller, the wideband sensor is not very useful. The controller also performs other important functions such as heating the sensor, so it gets to it's operational temperature much quicker (compared to waiting for it to heat up due to exhaust gas alone). OEM ECUs typically have a controller built in, but aftermarket ECUs usually have these as standalone boxes.
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