General Description

HO(2) (Oxygen) sensor
Two heated O(2) Sensors are used in the vehicle. The sensors produce voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust has in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air/fuel mixture), the sensors produce a low voltage. When there is a lesser amount (rich air/fuel mixture) the sensors produce a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors act as a rich-lean switch.

Both HO(2) Sensors are equipped with a heating element that keeps the sensors at proper operating temperature during all modes of operation. maintaining correct sensor temperature at all times allows the system to enter into closed loop operation faster and allows the system to remain in closed loop during periods of extended idle.

Front HO(2)sensor
The front (upstream) HO(2) Sensor is located in the exhaust down pipe after the TWC and provides an input voltage to the ECM. The input tells the ECM the oxygen content of the exhaust gas. The ECM uses this information to fine tune the air/fuel ratio by adjusting injector pulse width.

Rear HO(2) sensor
The rear (downstream) HO(2) Sensor is located near the outlet end of the catalytic convertor. The rear HO(2) 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 rear HO(2) Sensor input to the input from the front sensor, the ECM calculates catalytic convertor efficiency.