Downstream Oxygen Sensor

Fig. 19 Downstream Heated Oxygen Sensor:

DOWNSTREAM OXYGEN SENSOR - MANUAL TRANSMISSION
The downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor Fig. 19. The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency.