If your good with a multimeter and know which pins are which, you can set your meter to mV and watch the display. If its constantly changing (like 200-600mV) then the sensor is working. But if your not seeing any voltage or you are, but its not changing a lot or is reading way too high, then you have a bad sensor.
If you do decide to get a sensor, stay away from Bosch. They suck in our cars.