How does a downstream O2 sensor monitor converter efficiency?
A downstream O2 sensor in or behind the catalytic converter works exactly the same as an ?upstream? O2 sensor in the exhaust manifold. The sensor produces a voltage that changes when the amount of unburned oxygen in the exhaust changes. If the O2 sensor is a traditional zirconia type sensor, the voltage output drops to about 0.2 volts when the fuel mixture is lean (more oxygen in the exhaust). When the fuel mixture is rich (less oxygen in the exhaust), the sensor?s output jumps up to a high of about0.9 volts. The high or low voltage signal tells the PCM the fuel mixture is rich or lean. On some newer vehicles, a new type of ?wideband? oxygen sensor is used. Instead of producing a high or low-voltage signal, the signal changes in direct proportion to the amount of oxygen in the in the exhaust. This provides a more precise measurement for better fuel control. These sensors are also called ?air/fuel ratio sensors? because they tell the PCM the exact air /fuel ratio, not just a rich or lea
