Heated Oxygen Sensor

HO2S is a heat-type sensor which measures oxygen content of exhaust gases. ECM uses data from HO2S to determine air/fuel mixture. Sensors are positioned in exhaust system, ahead of and after catalytic converters. Using 2 HO2S allows ECM to monitor oxygen content in each cylinder bank individually.

The ECM regulates the amount of fuel injected per cylinder bank based on voltage signals received from the respective oxygen sensors. Oxygen sensor voltage varies from -.1 to 1.1 volts. When mixture is at rich threshold voltage should be .7-1.1 volts. When mixture is at lean threshold voltage should be -.1 to .3 volt.

Oxygen sensor after catalytic converter overrules oxygen sensor before catalytic converter. Oxygen sensor after catalytic converter serves as a corrective control. Oxygen sensor after catalytic converter makes slight corrections by holding oxygen sensor before catalytic converter control at high end of positive range (enrichment direction), or low end of negative range (lean direction) depending on need.