xp,
you don't need the sensor to go to 0.0V, it's only a switch. If it drops below .5V, you're lean, when you're above .5V you're rich. Typical values are 0.1-0.9. It doesn't matter if you're at 0.1 or 0.3, nor 0.8 vs 0.9, only above or below 0.5V matters.